If they are the original wheel cylinders, the bleeder screws are S.A.E. 3/8" hex head. If the cylinders are aftermarket, they are metric and a smaller size, but regardless which type and size, get a 6-point box-end wrench. May need to spray a little WD-40 on the screw threads first before attempting to loosen.
If you are bleeding brakes yourself without help, the easiest way to do it is with a Mity-vac and clear, flexible tubing of the proper size. Make certain that the master cylinder is full at all times while vacuuming fluid out through the wheel cylinder. When air bubbles no longer appear in the clear plastic hose, close the bleeder screw.