how to add WinJS 4.0 to visual studio 2013 as a reference

I am not able to add the newly downloaded WinJS 4.0 as a reference to my visual studio 2013. i already have WinJS 2.0. When i go to the add reference option and try to browse and add its looking for only (.winmd) files which is not available in the Winjs 4.0 package. Please help me with a step by step process.

Solution

I use NuGet Package Manager built-in Visual Studio to install the latest WinJS:

install-package WinJS

then I have to rewrite these files (if I'm using navigation app template) to use the new WinJS folder:

ui-themed.css (Windows Phone)
ui-light.css
ui-dark.css
default.html