Use the SaveFileDialog:
Private Sub myButton_Click(sender As Object, e As EventArgs)
Dim myStream As Stream
Dim saveFileDialog As New SaveFileDialog()
saveFileDialog.Filter = "Excel files (*.xlsx)|*.xlsx|All files (*.*)|*.*"
saveFileDialog.FilterIndex = 2
saveFileDialog.RestoreDirectory = True
If saveFileDialog.ShowDialog() = DialogResult.OK Then
xlWorkSheet.SaveAs(saveFileDialog.Filename)
End If
End Sub
Hope this helps,
Fredrik