Shut off the water supply
Flush the toilet to empty the tank and bowl
Disconnect the water supply line
Remove the old toilet if needed
Inspect the flange and drain opening
Install or replace the wax ring or seal
Set the toilet bowl onto the flange
Press the toilet down evenly to seat the seal
Secure the toilet with closet bolts
Reconnect the water supply line
Turn on the water supply
Check the tank fill and flush the toilet
Inspect for leaks at the base and supply connection
Caulk around the base if desired, leaving a gap at the back