How do I remove my existing shower drain?

It all depends on what type of shower and drain pipe you have. Can you post a picture? Some showers are mud pans made with mortart and those drains are set into the mortart and tile, break them out. Some showers have a PVC drain line and the drain is cemented to the pipe. Fiberglass shower pan may just have a rubber collar that slides over the pipe to create a seal. What do you have?