Removing the drain from the bathtub is beating me

what kind of stopper is in it? that decides the first step. lift-and-turn and toe-touch ones come off from the top - hold the cap, turn anticlockwise, and there's often a small screw underneath to undo. once the stopper is out you're looking at the drain flange, which threads into the shoe under the tub. a drain key does it, or the old trick of two plier handles crossed into the crossbars and turned anticlockwise with a screwdriver through them. if it won't move it's usually old plumber's putty, a hairdryer on it for a few minutes softens it. don't force it so hard you crack the shoe underneath - that turns a half hour job into opening the ceiling below.