The sample demonstrates how to Edit Excel in Silverlight via Spire.XLS.

<Application xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
             x:Class="Edit_XLS.App">
             
    <Application.Resources>
        
    </Application.Resources>
</Application>

using System;
using System.Windows;

namespace Edit_XLS
{
    public partial class App : Application
    {

        public App()
        {
            this.Startup += this.Application_Startup;
            this.Exit += this.Application_Exit;
            this.UnhandledException += this.Application_UnhandledException;

            InitializeComponent();
        }

        private void Application_Startup(object sender, StartupEventArgs e)
        {
            this.RootVisual = new MainPage();
        }

        private void Application_Exit(object sender, EventArgs e)
        {

        }

        private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
        {
            // If the app is running outside of the debugger then report the exception using
            // the browser's exception mechanism. On IE this will display it a yellow alert 
            // icon in the status bar and Firefox will display a script error.
            if (!System.Diagnostics.Debugger.IsAttached)
            {

                // NOTE: This will allow the application to continue running after an exception has been thrown
                // but not handled. 
                // For production applications this error handling should be replaced with something that will 
                // report the error to the website and stop the application.
                e.Handled = true;
                Deployment.Current.Dispatcher.BeginInvoke(delegate { ReportErrorToDOM(e); });
            }
        }

        private void ReportErrorToDOM(ApplicationUnhandledExceptionEventArgs e)
        {
            try
            {
                string errorMsg = e.ExceptionObject.Message + e.ExceptionObject.StackTrace;
                errorMsg = errorMsg.Replace('"', '\'').Replace("\r\n", @"\n");

                System.Windows.Browser.HtmlPage.Window.Eval("throw new Error(\"Unhandled Error in Silverlight Application " + errorMsg + "\");");
            }
            catch (Exception)
            {
            }
        }
    }
}

Imports System.Windows

Namespace Edit_XLS
	Partial Public Class App
		Inherits Application

		Public Sub New()
			AddHandler Me.Startup, AddressOf Application_Startup
			AddHandler Me.Exit, AddressOf Application_Exit
			AddHandler Me.UnhandledException, AddressOf Application_UnhandledException

			InitializeComponent()
		End Sub

		Private Sub Application_Startup(ByVal sender As Object, ByVal e As StartupEventArgs)
			Me.RootVisual = New MainPage()
		End Sub

		Private Sub Application_Exit(ByVal sender As Object, ByVal e As EventArgs)

		End Sub

		Private Sub Application_UnhandledException(ByVal sender As Object, ByVal e As ApplicationUnhandledExceptionEventArgs)
			' If the app is running outside of the debugger then report the exception using
			' the browser's exception mechanism. On IE this will display it a yellow alert 
			' icon in the status bar and Firefox will display a script error.
			If Not Debugger.IsAttached Then

				' NOTE: This will allow the application to continue running after an exception has been thrown
				' but not handled. 
				' For production applications this error handling should be replaced with something that will 
				' report the error to the website and stop the application.
				e.Handled = True
				Deployment.Current.Dispatcher.BeginInvoke(Sub() ReportErrorToDOM(e))
			End If
		End Sub

		Private Sub ReportErrorToDOM(ByVal e As ApplicationUnhandledExceptionEventArgs)
			Try
				Dim errorMsg As String = e.ExceptionObject.Message + e.ExceptionObject.StackTrace
				errorMsg = errorMsg.Replace(""""c, "'"c).Replace(vbCrLf, vbLf)

				System.Windows.Browser.HtmlPage.Window.Eval("throw new Error(""Unhandled Error in Silverlight Application " & errorMsg & """);")
			Catch e1 As Exception
			End Try
		End Sub
	End Class
End Namespace

<UserControl x:Class="Edit_XLS.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <Button Content="Run" Height="23" HorizontalAlignment="Left" Margin="314,248,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
    </Grid>
</UserControl>    

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.IO;

using Spire.Xls;

namespace Edit_XLS
{
    public partial class MainPage : UserControl
    {
        private SaveFileDialog saveFiledialog = null;
        public MainPage()
        {
            InitializeComponent();
            this.saveFiledialog = new SaveFileDialog();
            this.saveFiledialog.Filter = "Excel Documents(*.xls)|*.xls";
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            //create a blank workbook
            Workbook workbook = new Workbook();

            //edit the first sheet of the blank workbook
            Worksheet sheet = workbook.Worksheets[0];

            //Write string
            sheet.Range["A1"].Text = "String";
            sheet.Range["B1"].Text = "This text is written by Spire.xls";
            sheet.Range["B1"].HorizontalAlignment = Spire.Xls.HorizontalAlignType.Center;
            sheet.Range["B1"].Style.Font.Color = Colors.Red;

            //Write number
            sheet.Range["A2"].Text = "Number";
            sheet.Range["B2"].NumberValue = 1234.5678;

            //Write date
            sheet.Range["A3"].Text = "DateTime";
            sheet.Range["B3"].DateTimeValue = System.DateTime.Now;

            //Write formula
            sheet.Range["A4"].Text = "Formula";
            sheet.Range["B4"].Formula = "100*100";

            //Write richText
            sheet.Range["A5"].Text = "RichText";
            ExcelFont fontBold = workbook.CreateFont();
            fontBold.IsBold = true;
            ExcelFont fontUnderline = workbook.CreateFont();
            fontUnderline.Underline = FontUnderlineType.Single;
            ExcelFont fontColor = workbook.CreateFont();
            fontColor.KnownColor = ExcelColors.Green;
            RichText richText = sheet.Range["B5"].RichText;
            richText.Text = "Bold and underlined and colored text";
            richText.SetFont(0, 3, fontBold);
            richText.SetFont(9, 18, fontUnderline);
            richText.SetFont(24, 30, fontColor);
            sheet.Range["B5"].AutoFitColumns();
            sheet.Range["B5"].HorizontalAlignment = Spire.Xls.HorizontalAlignType.Center;

            //save the workbook
            bool? result = this.saveFiledialog.ShowDialog();
            if (result.HasValue && result.Value)
            {
                using (Stream stream = this.saveFiledialog.OpenFile())
                {
                    workbook.SaveToStream(stream);
                }
            }
        }
    }
}

Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Media
Imports System.IO

Imports Spire.Xls

Namespace Edit_XLS
	Partial Public Class MainPage
		Inherits UserControl
		Private saveFiledialog As SaveFileDialog = Nothing
		Public Sub New()
			InitializeComponent()
			Me.saveFiledialog = New SaveFileDialog()
			Me.saveFiledialog.Filter = "Excel Documents(*.xls)|*.xls"
		End Sub

		Private Sub button1_Click(ByVal sender As Object, ByVal e As RoutedEventArgs)
			'create a blank workbook
			Dim workbook As New Workbook()

			'edit the first sheet of the blank workbook
			Dim sheet As Worksheet = workbook.Worksheets(0)

			'Write string
			sheet.Range("A1").Text = "String"
			sheet.Range("B1").Text = "This text is written by Spire.xls"
			sheet.Range("B1").HorizontalAlignment = Spire.Xls.HorizontalAlignType.Center
			sheet.Range("B1").Style.Font.Color = Colors.Red

			'Write number
			sheet.Range("A2").Text = "Number"
			sheet.Range("B2").NumberValue = 1234.5678

			'Write date
			sheet.Range("A3").Text = "DateTime"
			sheet.Range("B3").DateTimeValue = Date.Now

			'Write formula
			sheet.Range("A4").Text = "Formula"
			sheet.Range("B4").Formula = "100*100"

			'Write richText
			sheet.Range("A5").Text = "RichText"
			Dim fontBold As ExcelFont = workbook.CreateFont()
			fontBold.IsBold = True
			Dim fontUnderline As ExcelFont = workbook.CreateFont()
			fontUnderline.Underline = FontUnderlineType.Single
			Dim fontColor As ExcelFont = workbook.CreateFont()
			fontColor.KnownColor = ExcelColors.Green
			Dim richText As RichText = sheet.Range("B5").RichText
			richText.Text = "Bold and underlined and colored text"
			richText.SetFont(0, 3, fontBold)
			richText.SetFont(9, 18, fontUnderline)
			richText.SetFont(24, 30, fontColor)
			sheet.Range("B5").AutoFitColumns()
			sheet.Range("B5").HorizontalAlignment = Spire.Xls.HorizontalAlignType.Center

			'save the workbook
			Dim result? As Boolean = Me.saveFiledialog.ShowDialog()
			If result.HasValue AndAlso result.Value Then
				Using stream As Stream = Me.saveFiledialog.OpenFile()
					workbook.SaveToStream(stream)
				End Using
			End If
		End Sub
	End Class
End Namespace