Remove the cover, called the strainer, from the current drain using a screwdriver. Slide the tips of a pair of pliers into the drain basket and turn the pliers counterclockwise to remove the drain. Slide the screwdriver through the handles of the pliers and use the screwdriver as leverage if the drain is stuck.
Remove the cover plate from the overflow hole on the tub by taking out the screw.
Connect the linkage to the new cover plate that comes with your pop-up drain assembly kit using a pair of pliers.
Rub a small portion of plumber's putty between your hands and create a circle out of it. Place the circle over the hole in the bottom of the tub. Press the new drain down onto the plumber's putty and screw it down clockwise using a pair of pliers. Rub away any extra putty with a rag.
Slide the overflow cover plate with the linkage attached onto the back of the tub. The linkage will hang down the back of the tub.
Slide the pop-up drain stopper into the drain, snaking the linkage into the drain pipe. The linkage is hinged so it will crawl up the back of the tub. Raise the overflow lever to lower the linkage attached to the overflow plate. The hook on the bottom of the linkage will catch the other linkage from the drain.