A shower drain threads into a pipe called a waste shoe that rests below the shower. When the plumber installed the drain, he used plumber's putty to seal it to the shower floor. If this seal leaks, mould will grow in your sub floor and eventually rot it out. Plumbers have a speciality tool to remove drains, but you can use a few household tools to take out the drain so you can replace the seal.
Remove the strainer from the top of the drain. To do this, slip the head of a screwdriver into one of the holes and turn it counterclockwise. If turning it does not work, pry it up. It could be a press-on strainer.
Place a pair of needle-nose pliers into the drain so each side of the pliers go into a different side of the metal X-shaped cross member inside the drain.
Place a large screwdriver between the handles and turn the screwdriver clockwise. The drain will turn with the screwdriver. It will take a bit of force at first, but once you completely break the seal, the drain will screw out easily.
Clean the plumber's putty out of the hole with a razor blade or putty scraper. Make sure you remove all of the putty from the hole before moving on. Wipe the hole dry and clean with a towel once finished.
Place a bead of plumber's putty around the edge of the hole and then thread the drain into the waste shoe with your fingers.
Insert the nose of the pliers into the new drain, place the screwdriver between the handles and tighten the drain into place.
Wipe off the excess plumber's putty and secure the strainer to the drain by threading it on or snapping it in place. Follow the directions on your brand of plumber's putty for drying times before using the shower.