Turn off the water supply valve behind the toilet
Flush the toilet to empty the tank
Hold the flush lever down to drain as much water as possible
Use a sponge or towel to remove remaining water from the tank
Disconnect the water supply line from the bottom of the fill valve
Remove the old fill valve locknut from under the tank
Lift the old fill valve out of the tank
Adjust the new fill valve height to match the tank
Insert the new fill valve into the tank opening
Tighten the locknut under the tank
Reconnect the water supply line to the new fill valve
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 on the new fill valve if needed
Flush the toilet and confirm proper operation