How to kill process and start another process

public static void ManageApp(string app, bool Shutdown)
        {
            Process[] processes;
            string File = "NONE";

            if (app == "GUI")
            {
                app = "VGUI";
                File = "V.exe";
            }

            if (Shutdown)
            {
                #region " Kill Vertex GUI "
                try
                {
                    processes = Process.GetProcessesByName(app);
                    foreach (Process proc in processes)
                    {
                       
                        proc.Kill();
                        proc.WaitForExit(5000);
                    }

                }
                catch (System.NullReferenceException) {/* no instance running */}
                catch (Exception ex)
                {
                    Console.WriteLine(app + " shutdown exception: " + ex.Message);
                }
                #endregion " Kill Vertex GUI "
                #region "Launch Vertex GUI Mimic"
                try
                {
                    ProcessStartInfo proc1 = new ProcessStartInfo("Gui_Mimic.exe");
                    proc1.Arguments = @"C:\Program Files (x86)\Sp\Ver";
                    Process.Start(proc1);
                }
                catch (System.NullReferenceException) { }
                catch (Exception ex)
                {
                    Console.WriteLine(app + " shutdown exception: " + ex.Message);
                }
                #endregion "Launch Vertex GUI Mimic"
            }
            else{ ..... Some things .....    }
         }