Change Multiple File Extension using Windows Form

//Please Fill free to ask query about this code,in case of error or have some changes  to make will be accepted.
//Thank you for using this code.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

using System.IO;                     //Use this Namespace.

namespace ClientOM
{
   public partial class ExtnChanger : Form
   {
      public ExtnChanger()
      {
         InitializeComponent();
      }
      private void btnclear_Click(object sender, EventArgs e)
      {
         txtpath.Text = string.Empty;
         txtnewext.Text = string.Empty;
         lblmsg.Text = string.Empty;
      }
      private void btnchngextn_Click(object sender, EventArgs e)
      {
         if (txtpath.Text == string.Empty || txtnewext.Text == "")
         {
            lblmsg.Text = string.Empty;
            MessageBox.Show("Directory Path/File Extension should not Empty.", "Info", MessageBoxButtons.OK,             MessageBoxIcon.Information);
         }
         else
         {
            try
            {
               string dirpath = txtpath.Text.ToString();
               string[] filepath = Directory.GetFiles(dirpath);
               foreach (string myfile in filepath)
               {
                  string filename = Path.ChangeExtension(myfile, txtnewext.Text);
                  System.IO.File.Move(myfile, filename);
               }
               MessageBox.Show("File Extension has been changed successfully.", "Success", MessageBoxButtons.OK);
               lblmsg.Text = string.Empty;
            }
            catch (Exception ex)
            {
               MessageBox.Show("Invalid Directory/Filename!", "Error", MessageBoxButtons.OK,MessageBoxIcon.Exclamation);
            }
         }
      }

      // To Validate TextBox
      private void txtpath_Leave(object sender, EventArgs e)
      {
         try
         {
            string dirpath = txtpath.Text.ToString();
            string[] filepath = Directory.GetFiles(dirpath);
            lblmsg.Text = "Directory Contains '" + filepath.Length + "' files inside.";
         }
         catch (Exception Ex)
         {
            lblmsg.Text = "Invalid Directory/Filename!";
         }
      }

       // To Validate Label
      private void txtnewext_Leave(object sender, EventArgs e)
      {
         lblmsg.Text = string.Empty;
      }
   }
}