Be brave! Remove the fixture handles first, including the cover of the shower mixing valve and the tub stopper. Remember to use a rag to plug the tub drain and keep debris out of your line.
You can do a shallow cut with a sawzall along the edge of the tub surround to loosen it. Them you can do similar shallow cuts vertically to remove sections of the surround. Be very careful around the shower control valve so you do not cut any of the supply lines. Those lines typically run vertically up from the floor (but not always). The shower head supply line runs vertically from the mixing valve, so it is easy to avoid. Study the diagram I provided before cutting.
If the tub is no cast iron (probably not) you can do the same operation to section it out.
Of course, you will want to turn off the water to your bathroom before doing any of this, just in case.
Plan on removing back to studs for the entire area. If you do not have access to the plumbing from behind the shower wall, now is the time to add access and shutoff valves for the future. The rebuild should include cement board (not drywall of any color), wall sealant such as RedGard, then whatever you want to do from there.