Here's how to replace old RV toilets with just a few tools and minimum instruction:
First, make sure the water to the RV is shut off. Then flush the toilet to reduce any pressure in the water line. If you'll look at the bottom of the toilet, you'll find a plastic cover going all around the base, or two of them, one on each side. Remove them.
Once the cover is removed, you'll see one or two bolts, depending on the model. Unscrew these, but don't lift the toilet just yet. Behind each of these types of toilets is a hose connected to the top back of the commode. Put a cloth under it to catch any water that may drip out, then unscrew the hose.
Now, remove the toilet from the floor, pulling up straight and making sure that the bolt stays upright in the floor. If the toilet is a bit stuck (this happens if a toilet has been in place a long time), simply rock it gently from side to side, then remove.
Now replace the rubber gasket that seals the toilet to the floor and put the new toilet firmly in place. Line up the toilet and bolt holes, screw the fixture down tight, then sit on the toilet to make sure it doesn't wobble. Tighten the bolts and screws a little more, and you're done!