Sometimes holding one part of the snap ring into the groove with plyers and prying with a screw driver on the open end you can snag the end of the ring and pry it up.
Just relax and, as Cal always would say, "You have to worry it off" after you do one, the next one will be easy. Dont poke yourself in the eye. Be careful.
I use a small screw driver to pry one end out a bit and then place a sharp awl against the edge of the drum pressing into the snap ring to hold the snap ring in place allowing the screw driver to get another bite on the end of the ring. Usually can get the awl behind the snap ring in three or so bites. Once the awl is in behind the ring the battle is won.