how do I delete an application?

I am new to QB so I testing with pre-built QB apps. When I am done with "experimenting" and have deleted such an app. because I have completely mis-understood some relationships, I have Deleted the app BUT when I want to get it again, the version QB returns has several of the changes I made in the previously downloaded application instead of a "clean" application...is there anything I can do to "scrub" my history?