Turn off the water supply to the toilet
Flush the toilet to empty the tank
Remove the tank lid and set it aside
Sponge out or drain any remaining water in the tank
Disconnect the water supply line from the bottom of the tank
Remove the old fill valve locknut from under the tank
Lift out the old fill valve
Insert the new fill valve into the tank opening
Adjust the fill valve height if needed
Tighten the locknut under the tank by hand, then snug it with pliers
Reconnect the water supply line
Attach the refill tube to the overflow tube
Turn the water supply back on
Check for leaks around the fill valve and supply connection
Adjust the water level using the fill valve adjustment screw or float
Replace the tank lid
Flush the toilet to confirm proper operation