A toilet's flange must be set at the proper height in relation to the finished floor in the bathroom, otherwise the toilet will inevitably leak. Often, a flange will be at the improper height because a new floor was installed in the bathroom. A new floor that is installed over the old finished floor will change the height requirements for the toilet's flange, as will a significantly thicker or thinner flooring material. You can purchase different sized extender rings for your toilet's flange to correct the problem.
Shut off the water flow to the toilet by turning the valve handle clockwise as far as you can. Flush the toilet once, then use an adjustable wrench to undo the nut holding the water line to the bottom of the toilet's tank.
Pry off the caps on the base of the toilet and remove the nuts on the closet bolts. Lift the toilet off the closet bolts and set it aside.
Remove the old wax ring and residue using a putty knife and mineral spirits. Place the extender ring over the flange and measure to make sure the extender ring sits between a quarter of an inch either above or below the finished floor.
Apply caulk to the bottom of the extender ring and place the ring over the flange, lining up the anchor screw holes in both. Drive the anchor screws through the extender ring and the flange, then clean up any caulk that presses out using an old rag.
Slide the heads of the closet bolts into the wider open slots in the extender ring, then slide the bolts along the channel and into the smaller notch in the ring. Press the wax seal onto the bottom of the toilet and then lower the toilet over the closet bolts, threading them through the openings in the base of the toilet.
Tighten the nuts onto the closet bolts and snap the caps over the bolts. Reattach the water line to the toilet tank using an adjustable wrench, then turn the water back on.