While you are certainly able to replace the toilet yourself, your local building codes may prohibit anyone but a licensed plumber from doing it. Before starting on a toilet replacement, contact your local plumbing professional to see if this is really something that you can or even want to do yourself. You just may decide on letting the expert plumber perform the work on this one.
Before you even purchase a new toilet, much less remove the old one, you will want to measure the distance from the wall behind the toilet bowl to the center of the toilet floor drain, to ensure that the replacement toilet that you get will fit into the same space. Shut off the water supply, remove all the water from the tank and bowl of the existing toilet. Disconnect the tank from the wall, if necessary, and the bowl; remove and set it aside. Disconnect the bowl from the floor hold-down bolts, plug the drain hole with a rag to prevent backup of sewer gases, then lift the bowl straight up to remove it. Inspect the uncovered drain and clear it if necessary. Check the floor and if any has been rotted, rebuild it before installing the new toilet.
On the water outlet opening on the bottom of the new bowl, install a new sealer ring using toilet bowl setting compound around the base edge of the bowl. Remove the drain plug and place the new toilet bowl down over the flange while guiding the bolts. Press down to seat the wax ring and make sure the bowl is level. Tighten the bolts, reattach the tank, and reconnect the water supply after ensuring that the ballcock assembly is attached correctly.
