Some people like to use a razor blade, but I prefer a razor blade paint scraper like this (most hardware stores sell them)
Carefully work the blade under the bezel & then continue around the circumference of the case. On some watches, it can take 20-30 minutes to work the bezel loose, but, eventually, it will start sliding up & you can then work it off the case.
Every once in awhile, you may run into a bezel that has been epoxyed onto the case, which can be a problem. But this is pretty rare with quality reps.