Where they interlock, push down on one side of the ring, and try to pull up on the other side with your thumb nail or a small precision screwdriver to unlock the ring. It takes a little bit of practice. Since you will not be reusing them, it is also OK to break a locking tang off with a small screwdriver, too. It is almost as much fun reinstalling the new rings. Again, push down on one side of the interlock, while pulling up on the other side, while pushing the ring together to overlap the tabs. This is where you do NOT want to break them. There is another smaller pair on the input shaft, too.
Be real careful when installing the output shaft into the rear support. I use Vaseline on everything here, especially the lead-in taper on the shaft support. This taper must compress the seal rings to allow the shaft to drop in. A bit of turning the shaft back and forth helps here. If the shaft gets dropped in without care, it can break one or both of the seal rings. You won't know until the trans is back in the car, and it won't shift out of LOW. Ask me how I know!