Unless you are very handy with tools and confident that you can do this yourself w/o doing harm to the weapon, I'd suggest two things:
First: consider sending the frame to Bill Springfield (http://www.triggerwork.net) and have him work his $49 trigger job magic (incl return shipping) on it. Then, when you get it back (mine turned around in a week), remove the magazine safety and the trigger will be worlds better and acutally feel like a real handgun trigger.
Second: contact Claude Wright (http://Guncrank.com) and tell him you want his Mosquito polishing package done on it. Tell him I sent you and he'll know exactly what you are talking about, I had him polish the chamber wall, chamfer the chamber opening (leaving the step intact, it really doesn't hurt anything being there), & polish the bolt face. I don't recall exactly what I paid him, but Claude's prices are extremely reasonable.
These two things done, and ~500 rds of CCI MiniMags for break in, and my Mosquito runs perfectly (barring ammo problems).
I only felt justified in spending the money on this pistol because I won it in a raffle and only had $2.00 in it from the begining, and I still say that any product bearing the SigArms name SHOULD NEVER HAVE HAD TO HAVE ANY OF THIS DONE. Shame on Sig for selling something this poorly executed! Once cleaned up and the problems corrected, it's a nice little pistol, but out of the box, it was a nightmare!
If you feel you must do this yourself, use the finest tooth file you can find (only if you feel the step must be taken off) and get an inexpesive Dremel tool and use the felt wheels and a bit of jeweler's rouge to do the polishing. Above all, be patient and work slowly, you can always take more off, but you can never put any of it back!