// Restart current process Method 1

System.Windows.Forms.Application.Restart();

Application.Current.Shutdown();  

// Restart current process Method 2

System.Reflection.Assembly.GetEntryAssembly();

string startpath = System.IO.Directory.GetCurrentDirectory();

System.Diagnostics.Process.Start(startpath + "\\xxx.exe");

Application.Current.Shutdown();  

// Restart current process Method 3

Process p = new Process();

p.StartInfo.FileName = System.AppDomain.CurrentDomain.BaseDirectory + "xxx.exe";

p.StartInfo.UseShellExecute = false;

p.Start();

Application.Current.Shutdown();