Kawasaki dot com & Partzilla have exploded parts diagrams. partzilla is easier to use.
Also, sometimes EB pics can be helpful on stuff like this.
I'm not familiar with the GPz 550 headlight, but after removing the screws there may be a couple of metal tabs that position the ring, so you may need to maneuver the headlight to clear the tabs or something like that. My headlight is round, so it's different, but almost every time it's almost like a new experience removing the darn thing. hee.
