My Answer: This is a little less information then I would have liked to have had, but I figured I would try to give an answer anyway. If you would like to replace your toilet, there are a number of things you should consider first. 1 If the toilet you are replacing has the tank mounted to the wall either just above the toilet or a high toilet tank mounted up above the toilet near the ceiling. You will need a special toilet to accommodate the toilet tanks. You will also need a toilet spud and a toilet slip ell to make this work. If you are going to replace toilet and toilet tank you can buy just about any toilet you like but you may find the new toilet tank is too far away from the wall. This is because in the old days there was no standard rough distances for the toilet drain from the wall because the slip ell was so adjustable it did not matter. So if you are replacing this type of toilet measure the distance from the wall behind the toilet to the center of the toilet drain. There are 3 standard rough in toilet sizes the most common is 12 inch so a 12 inch¯ rough in toilet will sit nicely close to the wall if the drain line is 12 inches to the center from the rough wall or 11 inches from the finished wall.
The other type toilet rough in sizes are 10 inch rough and 14 inch rough, these toilets are common but cost a little more and in some special colors designs can be very expensive or not available.
2 All new toilets are required to use 1.6 gallons of water or less. This can be a problem because the drainage systems are designed for 3.5 gallons per flush. Also some of the 1.6 gallon flush toilets clog all the time and need to be flushed more than twice defeating the water saving feature and annoying the hell out of people. There are great toilets that work well because they were designed much better I think Toto toilets are very good flushing toilets, there are many other good flushing 1.6 gallon toilets out there so do your homework to be sure you do not end up with a clogged toilet all the time.
3 Power flush toilets, they flush fast and clear the bowl fast. It has been reported that they splash allow of dirty water in to the bathroom air as a mist that makes everything in the bathroom dirty. It is very important to put the seat cover down before flushing a power flush toilet. Other problems I have had with power flush toilets are, in homes with back to back bathrooms where the toilets are tied into the same drain line with a cross TY fitting, when the power flush toilet is flushed in one bathroom the waste is blown out of the toilet in the other bathroom, a real mess.
Ok so now that you have some idea of what toilet to buy this is how to replace your toilet.
1 Check the strength of the floor around the toilet by pressing your foot all around the base of the toilet you want to replace, if the floor feels soft the wood around the toilet is dry rotted and will need to be replaced before you can install a new toilet. I find this problem in 1 out of 10 toilets I replace on non basement floor. (Even on tile floors)
2 If the floor is secure TURN OFF THE WATER then flush the toilet and hold the handle down to drain as much out of the toilet tank as possible. Wait a few minutes to be sure the water is off sometimes the water valve does not shut off 100% and the water will seep. Then remove all the water from the tank. Disconnect the water supply line, remove the tank from the bowl, (not absolutely necessary but does make it easier to carry)
3 Remove the caps over the bolts that hold the toilet to the floor, and then remove the nuts; many times the bolts will turn with the nuts, so you will need to cut the bolts just under the nuts to remove the toilet. You will not use the old bolts anyway. Once the nuts are removed, lift the toilet and put it someplace out of your way.
4 clean all of the old wax from the toilet floor flange and inspect the flange and the wood floor under the toilet floor flange. Make sure the slots that the new toilet bolts will slide under are not rusted out or broken, if they are it should be replace or a repair kit should be used. If the wood under the floor flange is dry rotted you will not be able to screw the flange down and the Toilet floor flange will come up when the toilet bolts are tightened and the toilet will not be secure to the floor.
5 Put the new toilet Johnny bolts in the slots of the toilet flange put the new wax seal on the new toilet bowl place the new toilet bowl over the flange making sure the new Johnny bolts come through the two holes in the new toilet base and press down evenly Find the new bold caps put the bottom of the bolt cap over the bolt first note it will say this side up then place the round or oval metal washed over the bolt next, then screw the new nut on top. Do not tighten the nut yet, follow the toilet manufacturer instructions to install the toilet tank to the toilet bowl, You may need to pull the toilet forward a little for the tank to fit, once the tank is installed step back and look to see if the tank and bowl are square and that the toilet is straight and square, adjust as needed then tighten the bolts, do not over tighten or you will break the new toilet bowl. Install the new water line. The braided metal flexible toilet supply lines are ok but the white plastic flexible toilet supply line will fail over time and you will have a flood. After you flush the new toilet a few times and you are sure you have no leaks, grout, caulk or plaster the base of the new toilet to the floor.