Ok, maybe silly question to a lot of you, but I found nothing telling me how. I downloaded several (Croft, Mid-Ohio, etc) and the files look nothing like the existing track files, and placing them in a folder and using the install mod tool..didn't even see them. (or I'm doing something wrong) This was always easy in RF1...lol
Options->unclick show mods only and you should be able to install. And use all cars tracks mode so you can race on those tracks.