1) Try something like goo-gone or goof-off, nearly anything chemical that will effectively remove the words will probably do some damage to the paint. These chemicals can only be used on metal, as they will likely melt plastic levers.

2) Try a sanding wheel on a Dremel tool. Sandpaper used manually could work just as well.

3) Look for some cheap wordless levers and replace the ones you have.

4) Use the sandpaper to break the surface of the words, then try the chemicals.