Depends on the type of pipe, cast iron, pvc, abs and how much access you have. It's one thing if it is buried in concrete, another if it is in a wood floor. Basically, you'd cut out the old stuff and redo with new getting everything to line up. How is the drain for the shower supposed to be connected? Is it a compression fit, a glued fit, etc. Is it designed for pvc? That will somewhat determine the material you use. Converting from one to another isn't a big deal. A few more details, and useful help can be supplied!