If your floor is showing excessive wear beyond normal cleaning, you might need to consider screening and recoating. Screening is used to abrade the polyurethane finish on the floor, then fresh coats of urethane are applied. Screening and recoating will rejuvenate and prolong the life of your hardwood floor.
If the damage to your floor is severe and has gone through the stain of the board down to the bare wood, you can sand and refinish. This should be done if a screening and recoating does not solve the problem. This is an extensive process where the floor is sanded down to the bare wood, restained, and then refinished. If the damage is only in a small area, you may want to see if replacement boards are available to alleviate having to refinish an entire area. Be sure to hire an experienced professional if this process needs to be done.