I know I suond like the biggest newb asking this, but i cant seem to get my taillights off.

I got the moldings off pretty easily, but for some reason theres a circluar nut on the bolts that hold the taillight in place. I have no idea how to remove te nuts, it seems like it would be equivalent to a 5/16th nut but it wont work, i tried pliers and vise grips but nothing does it.

I've been sanding my taillight panel tonight so its sorta imperative that i can get my taillights out so i dont damage them when i work around them. I can't see any other way to remove the taillights other than by taking the circular nuts off (which dont come off.) so i really don't have any idea how.