they have metal rails on the tops of them (when looking at body panel, the tops of the flares), which are screwed in to the panel, its not worth getting them off as when you go to put them on a different truck that didnt come with flares, you will either need to eyeball and drill holes, or pull the rails out of the flares (which usually warps the flare), and try to 3m tape them on the truck, which makes for a crappy look because they arent designed to be taped on.
I couldnt get to the back of the studs on the rails attached to flares from the backside of the body panels either, just pulled and broke the rail as I took the flare off.
*** But to answer your question, take all the screws out of the inside of the fender lips of all the flares, and pull them off and hope for the best with that damn rail.