Turn off the water supply to the toilet
Remove the tank lid and set it aside carefully
Flush the toilet to lower the water level in the tank
Disconnect the chain from the old handle lever
Unscrew the mounting nut inside the tank
Note that the nut may have reverse threads on some handles
Pull the old handle out from the outside of the tank
Insert the new handle through the hole in the tank
Tighten the mounting nut by hand
Attach the chain to the new handle lever
Adjust the chain so it has slight slack
Turn the water supply back on
Flush the toilet to test the new handle
Reinstall the tank lid