The vast majority of nipples are perfectly fine just the way they are. However, if your nipples have gotten excessively long, sag, and even point downward, and you want to shorten them, then this can be done surgically.
In general, there are two ways to perform a nipple reduction. Some surgeons will lop off the end of the nipple, allowing it to heal gradually from the outside inward. I am not a fan of this technique for obvious reasons.
Another technique, which I prefer, removes the excess nipple skin in a donut shape from the base of the nipple. The resultant “mushroom-like” end of the nipple is then sutured to the base, effectively shortening it. This does leave a permanent circular scar at the base of the nipple which usually heals really well. It can be done under a local anesthetic, although my patients prefer at least a little sedation to make it easier to tolerate.