While replacing a toilet isn't an everyday common plumbing task, it is one of those that involve a bit of complexity and takes more time. But you can do it by yourself if getting a bit dirty and smelling some bad gases doesn't frighten you. Make sure you know what you are doing; else, it would be a good idea to call a plumber and learn a bit while watching him, especially if it's your first time. In case you've got the courage to go with this challenge, then this small DIY guide will help you out.
For simplicity, this article will discuss only those toilets that come with a separate tank that is installed above the toilet bowl. If you have got any instructions manual from the manufacturer, this would be the time to go through it thoroughly. And it's always better to have an illustrated diagram of the parts with you.
To begin with, turn off the water supply to the tank and flush it twice to make sure that all the water goes down the drain. To be safe, you can use a sponge to dry any water still left inside the bowl or the tank.
Open the nuts and bolts that connect the tank with the bowl and the water supply line. Upon doing that, it will be easy to remove the tank. In case there is an elbow between the tank and the bowl, you will need to remove that first. Then, open the screws that are used to mount the tank to the walls. Do this step with extra care and hold the tank tightly in you hands, so that it doesn't fall when detached from the wall.
Now you have to remove the bowl, which is attached to the floor with some nuts and bolts. These bolts are usually hidden under caps, which you can take off by inserting a screwdriver beneath the caps and pushing them in the upward direction. The screwdriver should be covered with some tape, or it may scratch the surface of the bowl. Following the removal of the cap and nuts, the toilet bowl will be secure in its spot because of a seal with the floor. So rock it back and forth slowly and the seal would eventually break. Now you can take the bowl wherever you want but it would be a small weightlifting exercise.
Once the bowl is removed from its place, the toilet flange will be in the open. Shove some old, abandoned clothes inside so sewer gases would not escape into your house; This also insures that removable parts don't come off the flange. Next, get the new toilet and prepare for the installation; you will just need to put everything back in its place in the reverse order.
Take out the clothes from the flange and apply some plumber's putty to the bottom of the bowl, where it will come into contact with the floor. Now place the bowl such that its outlet would come exactly above the flange. The bolts won't fit in their place if you place the bowl wrongly. Once you have put it correctly into its position, ensure that it is in level with the floor. Now put the nuts and bolts in their respective positions and tighten them moderately. Fit the caps onto the bolts, and your new bowl is now in perfect shape. Next, line the tank up with the wall and put everything else in place in exact reverse order you removed it before. Now wash your hands, clean up the mess, and welcome your brand new toilet!