They are held on by sticky backing. Use a small flathead screwdriver or edge of a razor blade and pry the sticker out from one of the edges. You might need to use some sticker remover on the switch afterwards to get rid of the leftover adhesive before putting a new one on.
You can probably use Scotch clear double-stick tape on the back (they sell it in a standard tape dispenser, yellow in color) or use a little clear glue on it to reuse. I might have some legends lying around... anything you are looking for in particular?