There are two main types of pop-up drains used in bathtubs: the toe tap and the lift and turn type. The toe tap is so named because it can be easily lifted and closed (tapped) in with your toes while in the bathtub. The lift and turn type is opened, as the name suggests, by lifting up the stopper and turning to lock it in place. Both of these types of pop-up bathtub drains are relatively easy to disassemble.
Toe Tap Drain
Lift up the drain stopper so it is in the open position.
Place a towel or rag over the drain stopper; this will help keep it from being scratched.
Grasp the top of the stopper with the channel pliers. Turn the stopper counterclockwise until it screws out of the drain.
Lift and Turn Drain
Open the drain. Use the handle on the top to turn and lock it to the extended position.
Grip the top of the drain (the part beneath the handle) with a pair of channel lock pliers.
Grab the drain handle on top with the second pair of channel lock pliers. Use the first pair of pliers to hold the drain top steady, while the second pair turns the handle counterclockwise. You should feel the handle start to turn.
Pull the handle straight off the top of the drain. Pull the stopper out of the drain straight up.