Newer SIG P226s that have the forged stainless slide are fairly easy to swap out the hammer spring as they have a plastic spring retainer with a shorter spring which is easy to service.  Older models with the stamped slide have a hammer strut with a longer spring that can be a PIA to service as the spring is held under pressure by a small roll pin  that is pressed into the strut which requires an extra set of hands or some creativity to remove and replace.  Before attempting the latter, it might be a good idea to download the armorer's guide and/or order one of the better DVDs and first  review the procedure. 
HTH
Kevin

"I am a firm believer in therapy, for other people."
Kevin Schlier
Poconos, PA
http://www.brcv-gun.org