Place a towel over the drain. This prevents screws and other important assembly pieces from falling down the drain.
Unscrew the trip lever plate with a screwdriver. Trip lever plates are usually held together by two screws. Place the removed screws in a safe place where they won't roll away such as your pockets or a plastic bag.
Pull the trip lever plate from the wall slowly. The plunger assembly is attached to the plate. Pulling too quickly may damage the plunger assembly or the tub's lining.
Inspect the plunger assembly for corrosion or grime build up. Grime can be removed with a scouring pad and all-purpose cleaner. Remove moderate corrosion with a lime, calcium and rust cleaner. Severe corrosion ruins the structural integrity of the plunger assembly. In this situation, the assembly must be replaced.
Shorten the plunger's length by twisting the plastic adapter directly above the plunger's weight (this is the large object at the bottom of the assembly). Continue twisting until the plunger assembly is shortened by a quarter inch.
Insert the drain stopper plunger assembly back into the wall and screw the trip lever on. Turn on the water and test the drain stopper. Readjust the length of the plunger assembly again if problems persist.