you need a heat gun (to heat up the fender lips and the paint so the paint doesnt crack and it bends more fluid), a rubber mallet (to actually hit the fender lip with), and about two hours max.
heat up the fender lip (this is done best with the wheels off so you can sit nearly inside the wheel well) so that its hot to the touch. you wont screw up the paint getting it hot, the sun does it all the time. start by hitting the fender softly and gradually getting harder until you can tell how hard you need to actually hit it to get it to go where you want. its surprisingly takes a good whack at it to do much. work your way back and forth on the fender basically doing the entire lip at once so that it doesnt crease or do anything funny. KEEP THE PAINT HOT. do this until the once 'L' shaped lip is more of a 'V'. youll see what im talking about when you look at it. this is what you would call fender rolling.
NOW, if you go really big and or low offset you may have problems with rubbing even with your fenders rolled. that is where you could maybe get a new set of wheels or try one more thing: pulling the fenders. when you PULL the fenders you literally pull them out farther and basically bend them out more to get more clearance. pulling the fenders is MUCH harder to make look clean as its super easy to put creases in the fenders. also, if you pull the front fenders too much you get a noticeable gap between the fender and the door, which is not a good look.
any more questions, ace? please hit the tanks button.