Lift the stopper lever. Grab each side of the raised stopper and pull it from the drain hole.
Insert the rocker arm of the replacement stopper into the drain hole. The rocker arm resembles a sort of tail on the underside of the stopper. Force the stopper and its rocker arm down into the drain.
Lower the stopper lever. Run bath water to check whether the stopper forms an effective seal. If necessary, proceed to adjust the stopper height.
Drain the bath water and remove the stopper for adjustment.
Loosen the locknut below the head of the stopper using needle nose pliers.
Rotate the stopper head clockwise one to two turns, then tighten the locknut once again.
Insert the stopper back into the drain. Test whether the stopper closes sufficiently to prevent water draining from the tub. If necessary, adjust the stopper height further.
Raise the stopper lever. Pull the old stopper free of the drain hole.
Fit the rocker arm of the replacement stopper into the drain hole. The rocker arm extends from the bottom of the stopper. Push the stopper and its rocker arm down into the drain.
Close the stopper. Run water from the spigot into the tub. If the stopper fails to close sufficiently, allowing water into the drain, proceed to adjust the lift rod.
Remove the screws from the stopper lever cover plate. Remove the plate along with the lift assembly attached to the backside.
Loosen the locknut below the assembly lift rod using needle nose pliers. Rotate the rod clockwise three to four turns, before tightening the locknut.
Reinstall the lift assembly and cover plate. Do not reinstall the screws just yet. Instead hold the cover plate in place.
Test the stopper once again to determine whether it closes tightly enough to keep water inside the tub. If necessary, adjust the lift rod further. Otherwise, reinstall the stopper lever cover plate screws.