Sometimes you have to cut the fiberglass shower stall to remove it. Other times, there's a window or other obstruction that you need to cut away from the fiberglass shower stall. Either way, fiberglass is tough to cut, so prepare for a little exertion when you attempt the job. Cutting a fiberglass shower stall to fit into a space requires that you take precise measurements and mark the spot carefully. Use the rule of thumb when you cut it: always measure twice and cut once.
Take the measurements if you're cutting the fiberglass to fit in an area. If you're going to make any mistakes, it's better to cut too little away. This is also a problem since it's difficult to cut small slices of fiberglass.
Put on a mask and safety glasses before you do any cutting. The process releases small fiberglass pieces, and these are dangerous. You don't want to get any into your eyes, nose or lungs. Consider wearing a cheap raincoat with the wrists taped and a painter's hat to keep the fiberglass dust off you. Wear gloves.
Be aware that some manufacturers of fiberglass shower stalls insert a layer of gypsum between the layers of fiberglass to give it more rigidity. When you hit that layer, you'll notice a cloud of dust from the gypsum. Stop when the dust starts and have a wet/dry shop vacuum ready to suck it away. You also should have a fan going aimed toward an open window, if possible, to eliminate as much dust as possible.
Select the right type of saw when you cut a fiberglass shower stall. Remember that the fewer teeth in your blade, the coarser your cut. You can use a reciprocating saw or a jigsaw to make the cut. If you don't care how the finish looks because you're cutting out the fiberglass, any blade will work. The coarse blades with fewer teeth are for wood. A metal cutting blade creates a finer cut. You'll have more problems controlling the blade if it's for wood, but it's faster than the metal blade and there's less dust. Hacksaws also work.
Try a router to cut the fiberglass shower stall if you're just removing it. Use a small router. Set the blade to the thickness of glass. You'll eliminate kickback this way. Simply bend away the corners, since the router won't cut them.
Remove your clothing as soon as possible to prevent to fiberglass from irritating your skin after you cut the fiberglass shower stall.