Disassemble and remove bathtub–shower combination
You will need to cut the drywall away from the edge of the tub and surround.  The drywall should overlap a flange of the tub/surround.  That should expose the screws and clips holding the tub and surround to the studs.  If you are lucky, the installer didn't also use glue to attach the surround to the studs as well.

Found link to install instructions.  http://www.homedepot.com/catalog/pdfImages/cf/cf84df47-d48f-4392-80e4-79ec296343ad.pdf