Upload Gridview To Excel - Allow User To Select Where To Download The File

I have a gridview that allows the user to export this gridview to excel. Here is my codes but I would like my user to be able to select where to download the file

Protected Sub ExportToExcel(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnExport.Click
lblMsg.Visible = True
Try
Dim objSw As New StreamWriter(txtFileName.Text.Trim + ".xls")
'Dim serverFilePath As String = "D:Excel Files"
'Dim fileStream As New FileStream(serverFilePath, FileMode.Open)
'Dim fileSize As Long = fileStream.Length
'Response.ContentType = "application/octet-stream"
'Response.AddHeader("Content-Disposition", "attachment; filename=""" & txtFileName.Text.Trim & """;")
'Dim fileBuffer As Byte() = New Byte(fileSize - 1) {}
'fileStream.Read(fileBuffer, 0, CInt(fileSize))
'Response.BinaryWrite(fileBuffer)
'fileStream.Close()
'Response.[End]()
Dim objDt As DataTable = DirectCast(Session("Data"), DataTable).Copy()
'Get No Of Column in GridView
Dim NoOfColumn As Integer = objDt.Columns.Count...........................