You or a professional floor refinisher can tackle the job. If the task is yours, be sure to properly prepare the area and you.
Sanding produces highly flammable dust, so remember to seal the doorways into your work area with plastic and ventilate the area with a fan. While sanding, wear goggles, ear protection and a dust mask. And when applying the finish, wear goggles, rubber gloves, long pants and a long-sleeve shirt, for added protection.
Keep in mind that the goal is NOT to sand through the finish, but to lightly sand the top coat until the finish feels smooth.
Once the floor is completely dry, apply a single coat of polyurethane finish. For a waxed floor, apply a mineral-spirit based renovating product and buff with a No. 1 steel wool pad. Allow the floor to dry completely, then wax and buff. These steps will brighten the appearance of the finish, not lighten the wood itself.