Help! Xbox live won't let me download certain content!!?

Ok so if I try to download something thats rated M on the xbox live marketplace it brings up a box that says "this account is not permitted to download content with this rating" so I was wondering if there is a way I can chAnge my settings or something to allow me to download this content. Also I want to download map packs but I don't want to buy marketplace points and have it not let me download the lap pack. So will it let me or no?? Thanks!