First, put on your safety glasses and gloves. If old closet bolts are present, remove them by sliding them out of their slots. Use a putty knife to carefully scrape off all remnants of the old wax ring from the top and inside of the flange. Deposit the old wax into a bucket or onto a piece of cardboard for disposal. After removing the bulk of the wax, use rags, possibly dampened with a small amount of mineral spirits or a degreaser, to wipe the flange completely clean. The goal is a clean, dry, and debris-free surface for the sealant to adhere to.

Place a straightedge or level across the drain opening, resting on the finished tile floor. Use a tape measure to measure the vertical distance from the top of the existing flange to the bottom of the straightedge. This measurement determines the required thickness of your extender(s). Based on our assumed 1/2-inch gap, you will likely use one 1/2-inch extender or two 1/4-inch extenders. Place the selected extender(s) on the flange without any sealant. Check that the screw holes and closet bolt slots align properly with the holes and slots on the original flange.

After confirming the dry fit, remove the extender(s). Load the tube of 100% silicone sealant into the caulking gun. Apply a continuous, generous bead of sealant (about 1/4 to 3/8 inch thick) directly onto the clean top surface of the existing flange. If you are stacking two extenders, apply a similar bead of silicone to the top of the first extender before placing the second one on top.

Carefully place the flange extender onto the bead of silicone, pressing down firmly and evenly to spread the sealant. Align the screw holes and closet bolt slots with those on the flange below. Insert the long screws provided with the extender kit through the countersunk holes in the extender. Using a drill with a screwdriver bit or a manual screwdriver, drive the screws through the extender, through the original flange's screw holes, and securely into the wood subfloor below. Tighten the screws until they are snug, alternating between screws to apply even pressure. Do not overtighten.

Take the new, longer closet bolts (usually included in the extender kit) and slide the heads into the closet bolt slots on the topmost extender ring. Position them at the 3 o'clock and 9 o'clock positions, parallel to the back wall. Use the plastic retainer washers that came with the bolts to hold them upright and in place. Next, take the new wax ring and place it over the flange. Press down gently but firmly on the wax ring to create a slight seal against the top of the extender. This ensures it stays in place as you lower the toilet.

Using a rag or paper towel, carefully wipe away any excess silicone sealant that may have squeezed out from the sides of the extender. This provides a clean, professional finish. Allow the silicone to cure according to the manufacturer's instructions (typically 12-24 hours for a full cure) before subjecting the area to heavy use, although the toilet can generally be installed immediately. The flange is now at the correct height and is ready for the toilet installation to be completed.