Hi,
Namespace --> Using System.Configuration;
System.Configuration.Configuration appConfig=System.Configuration.ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
appConfig.Appsettings.Settings.Remove(sConnectionKey);
appConfig.Appsettings.Settings.Add(sConnectionKey,sNewValue);
appConfig.Appsettings.SectionInformation.ForceSave=true;
ConfigurationManager.RefreshSection("Appsettings");
appConfig.Save(ConfigurationSaveMode.Full);
ConfigurationSettings.Appsettings[sConnectionKey]=sNewValue;
Here
sConnectionKey --> Key Name in Config File
sNewValue --> Its your New Connection Value
Thanks,
T.Saravanan :)