If there is a reason I don't see it, unless it's due to the way crash damage is handled (but then why did it work before?)

So can someone now tell me how to delete custom cars from ingame. I have downloaded a few and made/registered their packs. Now I haven't a clue how to delete them. When I go to manage packs, it does not give me an option to delete a previous cutom pack/car I already have in there.

Deleting the files for the applicable car or skin in "Documents\ManiaPlanet\Skins\Vehicles\CanyonCar\" doesn't work?