A toilet bowls sits on top of a closet flange, which in turn is screwed to the bathroom floor. Between the two rests a wax ring that seals the toilet bowl to the flange and prevents leaks. The weight of the bowl squashes the ring, which creates the watertight seal. The required thickness of the ring is determined by the positioning of the flange.
Turn the water off to the toilet at the shutoff valve located under the toilet tank. Flush the toilet once to remove water from the tank and bowl. Unthread and remove the flexible water supply hose connected to the bottom of the tank.
Remove the nuts attached to the vertical bolts that pass through the holes on each side of the toilet bowl base. Take off the washers. Carefully lift the toilet up and out of position.
Scrape off the old wax ring that sits on top of the closet flange. Study the lip of the closet flange screwed to the bathroom floor: If the lip is higher than the surrounding floor, a standard wax ring is needed. If the flange lip is flush with the floor or lower than the surrounding floor, one of three choices can be made. Place one standard wax ring on top of the other. Secondly, use a wax ring that is thicker than a standard ring (though the diameter will be the same). Third, use a wax ring with a plastic bell attached to the bottom. This ring is thicker than a standard ring, though generally used in older homes where no closet flange has been installed.
Rest the new wax ring on the flange, with the both flange and wax ring holes lining up. Lower the toilet into position. The vertical bolts on the sides of the wax ring enter up through the holes on each side of the toilet bowl base. Push down slightly on the toilet to squash the ring against the flange and bowl.
Place the washers back on the tops of the bolts. Tighten the nuts onto the bolts. Reattach the flexible hose to the bottom of the toilet tank.