Whenever I'm faced with an issue like that, I just start unbolting things until I figure it out. The one piece levers should come off with just one bolt. Having owned a few dirt bikes, I got good at replacing levers, since they usually break about once out of five crashes, and I usually average a couple of minor crashes per ride up in the hills. In fact, I used to keep a bag of broken levers, in case I needed one that was in a little better shape than the one I just broke off.
If you have the newer 2-piece levers, leave the inner piece in place and just remove the outer part. It's an easy job that way.