Asp.Net not only create a text file on client but also delete it

protected void btNotepadPending_Click(object sender, EventArgs e)
{
    string sFileName = System.IO.Path.GetRandomFileName();      
    try
    {
        String testo = "XXX" + Environment.NewLine;
        int iii = 0;
        foreach (var item in lUserPending)
            testo += ++iii + " - " + item.Item1 + " " + item.Item2;


        //Create and populate a memorystream 
        MemoryStream mstream = GetTextAsStream(testo);

        //Convert the memorystream to an array of bytes.
        byte[] byteArray = mstream.ToArray();

        //Clean up the memory stream
        mstream.Flush();
        mstream.Close();

        // Clear all content output from the buffer stream
        Response.Clear();

        // Add a HTTP header to the output stream that specifies the default filename
        // for the browser's download dialog
        Response.AddHeader("Content-Disposition", "attachment; filename=delenda.txt");


        // Add a HTTP header to the output stream that contains the
        // content length(File Size). This lets the browser know how much data is being transfered
        Response.AddHeader("Content-Length", byteArray.Length.ToString());


        // Set the HTTP MIME type of the output stream
        Response.ContentType = "application/octet-stream";

        // Write the data out to the client.
        Response.BinaryWrite(byteArray);
        Response.Flush();
        Response.Close();
    }
    catch (Exception exc)
    {
        MessageBox.SendErrorEmail("Exception: " + exc);
    }
}

private MemoryStream GetTextAsStream(String text)
{
    //Create the return memorystream object
    MemoryStream ReturnStream = new MemoryStream();

    //Create a streamwriter to write to the memory stream
    StreamWriter WriteStream = new StreamWriter(ReturnStream);

    //Write the text in the textbox to the Memory Stream.
    WriteStream.WriteLine(text);

    //Clean up the stream writer
    WriteStream.Flush();
    WriteStream.Close();

    //Return the memory Stream
    return ReturnStream;

}

protected override void OnUnload(EventArgs e)
{
    if (IsPostBack)
    {
        if (File.Exists("delenda.txt"))
            File.Delete("delenda.txt");
    }
}