The project has two separate directories to help leverage the use of built-in chips. Don't modify the directory structure -- your RAM512, RAM4K, RAM16K should be in the "2" directory.
Given that you haven't modified the layout of the project, loading RAM4K should not "take forever" to load.
To answer your question (how do I use the built-in chips?), your .hdl implementation will use a built-in chip given that a corresponding .hdl definition for the chip you wish to use does not exist in your current working directory.