Changing Connectionstring string at runtime

for appsetting 

  Configuration configFile = ConfigurationManager.OpenExeConfiguration(Application.ExecutablePath);
            configFile.AppSettings.Settings["User"].Value = "Hello World"; //User is the key variable name
            configFile.Save();

for ConnectionString 

 Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            config.ConnectionStrings.ConnectionStrings.Remove("MyConnection");
            config.ConnectionStrings.ConnectionStrings.Add(new ConnectionStringSettings(
                                                          "MyConnection",
                                                          String.Format("Provider={0};Data Source={1}",
                                                                         "Microsoft.JET.OlEDB.4.0", "D:\\Database\\EQMAN.mdb")));
            config.Save(ConfigurationSaveMode.Modified, true);
            ConfigurationManager.RefreshSection("connectionStrings");