To manually upgrade an existing ASP.NET MVC 3 application to version 4, do the following: In all Web.config files in the project (there is one in the root of the project, one in the Views folder, and one in the Views folder for each area in your project), replace every instance of the following text: System . Web . Mvc , Version = 3.0 . 0.0 System . Web . WebPages , Version = 1.0 . 0.0 System . Web . Helpers , Version = 1.0 . 0.0 System . Web . WebPages . Razor , Version = 1.0 . 0.0 with the following corresponding text: System . Web . Mvc , Version = 4.0 . 0.0 System . Web . WebPages , Version = 2.0 . 0.0 System . Web . Helpers , Version = 2.0 . 0.0 , System . Web . WebPages . Razor , Version = 2.0 . 0.0 , In the root Web.config file, update the webPages:Version element to "2.0.0.0" and add a new PreserveLoginUrl key that has the value "true": <appSettings> <add key = "webpages