From what I see in the factory manual there is a whole butt-load of rivets on the back piece. I suggest you remove the gutter sealer back there. Then drill out the rivets. The back piece looks like it should slide off. then, The other pieces should come off pretty easily once you slide them to the rear a bit to disconnect them from the more forward pieces.
Now I'm saying this just based on what I see in the pictures. I do need to remove mine as well. One of these days......
Good luck.