here is what I experienced: (before I begin... kudos to devnull for the answer).
I clicked on:
1) View -> Other windows -> Package Manager Console then ran
2) install-package entityframework -version 5.0.0.0.
The uninstall started, but then rolled back, as it detected I already had installed Entity Framework (EF) 6.0.2 ...
>PM> install-package entityframework -version 5.0.0.0
Installing 'EntityFramework 5.0.0'.
You are downloading EntityFramework from Microsoft, the license agreement to which is available at http://go.microsoft.com/fwlink/?LinkId=253898&clcid=0x409. Check the package for additional dependencies, which may come with their own license agreement(s). Your use of the package and dependencies constitutes your acceptance of their license agreements. If you do not accept the license agreement(s), then delete the relevant components from your device.
Successfully installed 'EntityFramework 5.0.0'.
*****Install failed. Rolling back...*****
install-package : Already referencing a newer version of 'EntityFramework'.
At line:1 char:1
+ install-package entityframework -version 5.0.0.0
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Install-Package], InvalidOperationException
+ FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand
So then I uninstalled the Entity Framework 6.0.2 and found it had a dependency that also needed to be removed... then I was finally able to uninstall the Entity Framework 6.0.2 and then add the Entity Framework 5.0.0.0
PM> uninstall-package entityframework -version 6.0.2
uninstall-package : Unable to uninstall 'EntityFramework 6.0.2' because 'AnotherFakeDbSet 3.0.0.0' depends on it.
So then I uninstalled these two and installed Entity Framework 5.0.0.0
PM> uninstall-package AnotherFakeDbSet -version 3.0.0.0
PM> uninstall-package entityframework -version 6.0.2
PM> install-package entityframework -version 5.0.0.0
I like the console... quicker than searching for the packages if you know the version #. And if you haven't checked out "Powershell" (the basis for the console -- I find it's time well spent - it allows for virtually unlimited automation)