Two things to check:
1- Are the loads the same as the pistol was set up to fire? Typically, if the POI is way low, you are shooting higher velocity/lower bullet weight ammo than the pistol was designed for. Not a problem, really, but it would be the first thing I would check. If you intend to keep shooting that ammo, go to #2, otherwise just change ammo.
2- If the front sight is too high or the rear too low, either replace the rear sight with a taller sight, or lower the front sight by removing some off of the top of the sight. I prefer to replace the rear sight, it's easier to fix and change, and you don't have the "ooooooops!" or the disappearing front sight issues.