Can I make this bike more off road worthy?

I want a hybrid bike that can handle some light trails. If I have 700c tires on say, the Trek 7.2 FX, can I change the wheels or even just the tire to make it handle better off road? Or is there something more essential that makes the 7.2 a strictly street bike?

I live in the city and need a communter that I can also have fun with.