As monk said, be very careful with any exercise that is intended to increase your hand span. There are several threads on this forum that deal with this issue, but I'll repeat what I usually say to this topic.
The "true" handspan is determined at your wrist, i.e. where the fingers attach to the wrist bones. A very simple exercise is stretching the hand by closing it (making a fist) and opening it to its fullest. Hold it for a few seconds in this state. As with most stretching exercises, you'll feel strong tension initially that then slowly subsides and actually gives a pleasent sensation at the end. Don't overdo this, because you can dislocate joints and injure tendons. Remember, stretching is supposed to stretch muscles, not tendons. However, this exercise can be done throughout the day, and it does help a bit. If nothing else, it makes your wrist more supple.
The second aspect is the span between the fingers at the knuckles. Cutting the skin is one way to remove the limiting effect of that skin. A less drastic way is to massage the tissue between the knuckles. Over time, this will soften the tissue and increase the span.
The third alternative, which I prefer, is to let the span get larger on its own through normal playing and use the "cheating" techniques that will allow you to play large chords with small hands. Lots of people do that, and I have never heard of a pianist being slammed because s/he didn't have span like Rachmaninoff.