The rings are held on by 4 clips and one screw. The clips are at 1,4,7,10 O'clock positions and the screw is located at the 9 position.
The screw head will break through the bumper when you pry the ring off but this isn't any big deal as the clips will hold on your new rings fine.
Heres a pic of the back of the ring.
Heres a pic of the bumper with the ring off.
Place a small pocket screwdriver on the inside of the ring. Put it in far enough so you hit the outer lip of the ring itself. Push the end of the screwdriver towards the light itself thus popping off that part of the ring. I recommend putting the screwdriver next to each clip and popping off one clip at a time.
Heres a pic of where the screwdriver should be placed.
Enjoy your new rings! DD