Measure the toilet to ensure it fits, thoroughly clean any wax seal remnants from the bottom of the toilet, place a new wax seal over the sewer pipe in the floor, lower the toilet onto the seal and bolt the toilet to the floor are the steps to installing a used toilet. Reconnect the water lines to use the toilet. Other than cleaning the old was seal the steps are the same for a new toilet.
Not all toilets are the same size from the disposal drop to the back of the tank. If there is not enough room between the waste hole in the floor and the bathroom wall, the replacement toilet can't seat properly. Remove the old toilet to take an accurate measurement.
Turn off the water supply and disconnect the water line to the old toilet. Remove the bolts holding the toilet to the floor. Lift the old toilet off of the floor and set it out of the way. Toilets are heavy so get a helper to assist you. If the old fixture is stuck to the floor by the wax seal use a putty knife to free it. Chip away all of the old wax from around the drain in the floor and measure the distance from the wall to the edge of the drain closest to the wall. Install the replacement toilet if it fits.