If you need to shorten the front sight, here are a couple of options:
Find something hard and flat to place over the rear sight. Use that as a guide to to file the sight. You can also cover the rear sight with tape, cover the rear half of the file with tape (one piece parallel with the file. Rub a little grease on the tape and lay it on top of the rear sight as guide. The trick is to be CERTAIN the file is square with the front sight.
The easiest method is to use a drill press. Remove the slide and place in a machinist's vise. Place the vise on the drill press platform. Chuck a small flat grinding wheel in the drill and trim away. I use a Dremel wheel. Again, the trick is to be sure the surface of the grinding wheel is square with the front sight.
I have successfully used both methods. If you need, I can email a couple pixs.