I've levered a few off, the clips sure shoot a long way when they finally give in.
The other way is using side cutting pliers and cutting at the narrow bits to make the clip into 2 pieces. Then either replace with circips or the speed washers - I have heard some people install them with a right size round steel pipe, or ratchet socket (somewhere between 12 and 16 mm) and give the new clip a tap with the hammer.
I think they are called star lock washers from memory.
