Designing Kitchens and Bathrooms - removal of fiberglass shower pan

How do I remove the nut(?) from the drain in order to remove the shower pan. I have already removed the tile and wallboard and I am down to the studs. Is a special tool required? What is holding the pan in place at the drain? I am assuming there is some kind of a nut. Thank you for any suggestions you might offer.

Depending on how old the shower pan is, most of the ones we use today are just connected with a rubber barbed sleeve, and the pan will pull off the pipes without incident. Now, if you are sure there is a nut, there is a tool that looks like a double forked cast aluminum widget. There are actually 4 tools in one, depending on the type drain you have. One of the ends will fit into the drain and turn the inner ring, unscrewing it from the base. Post back and let us know how it goes, and if we can help further.