For Visual Studio 2010 Web based application we have Config Transformation features by which we can maintain multiple configuration files for different environments. But the
If you use a TFS online(Cloud version) and you want to transform the App.Config in a project, you can do the following without installing any extra tools. From VS => Unload the project => Edit project file => Go to the bottom of the file and add the following:
AssemblyFile and Destination works for local use and TFS online(Cloud) server.