I upgraded form MVC4 to MVC5 by following the steps at this link
How to Upgrade an ASP.NET MVC 4 and Web API Project to ASP.NET MVC 5 and Web API 2
that walk you through steps to upgrade from MVC4 to MVC5
Here is a quick summary of the upgrade steps.
Backup your project, as it upgrade will involve changes to package configuration and web.config files.
upgrade from Web API to Web API 2 by making some changes in
Make sure all the packages that your projects use are compatible with MVC 5 and Web API 2. They provide a table of package versions from Microsoft packages
Open project in Visual Studio.
Using Package Manager Console (PMC), remove certain ASP.Net NuGet packages if installed.
Upgrade all the ASP.Net NuGet packages using the PMC
They show how to: Update the
Application web.config File and
Update the web.config files under the Views folder
Check out the link and see if that helps.