Replacing a bathtub drain is relatively easy. First you need to identify the type of drain you have. Does yours have a built-in stopper or is it an open drain? Once you have that information, you need to go to the hardware store and pick up a new bathtub drain kit. When that is purchased, you will be ready to replace your bathtub drain.
To assemble your new drain, you will need to have some Teflon tape for the actual kit. Also get a tube of clear silicone caulking and a caulking gun. Have a sheet or something equivalent that you can place inside the bathtub so you do not scratch it while working inside it.
Remove Old Drain
At the top of your tub above the drain is a metal cover. Take out the two screws holding it and remove it. Now you can see the inner part of your drain. Going through the access panel in your wall, you should be able to pull down and lift the old drain from the tub. After the drain mechanism is removed, go back in the tub and remove the old flange. Clean the area around the drain hole and the upper cover panel.
Install the New Drain
Assemble the new bathtub drain kit according to the instructions. Remember that you may have to cut the drain assembly overflow pipe so it fits your tub. Dry fit the new unit to the tub and then make adjustments where they are necessary. After the adjustments are made, you can permanently assemble the drain kit using Teflon threads on any threaded connections.
Have a helper position the drain unit to the tub and hold it while you are inside the tub. Place a thin bead of silicone caulking on the new drain basket and screw it into the new drain. You will be threading it onto the new drain and you can tighten it with a pair of pliers holding the cross-hairs. Assemble the stopper linkage to the cover plate. Most PVS linkages will come in two pieces and one will thread into the other. It is made this way to allow for length adjustments if necessary. Dry fit it to make sure the stopper rests at the T-joint when closed.
With adjustments made, apply a thin coat of silicone to the cover plate and thread the linkage down the overflow pipe. Tighten the mounting screws on the cover plate to the tube.
Attach the drain cover and your new bathtub drain is complete.