How can you make sure that classes in PassGuideApp references the latest version of the class library types?

DRAG DROP
There is an ASP.NET Web site PassGuideWS.
You use ASP.NET Web application template to create a new application, PassGuideApp, in
a new Visual Studio solution.
Types in the class library project is used. The source code of this library is used often.
How can you make sure that classes in PassGuideApp references the latest version of the
class library types?