Tub surrounds are often purchased in large panels that are easily installed along the walls above a tub. These styrene or high-impact styrene plastic tub surrounds are simple for most homeowners to install. One problem that homeowners may face is installing a tub surround when there's a window above the bathtub. Most tub surrounds are not made to fit around window, so homeowners have to learn to how to cut the tub surround to size before installing it.
Mark the area you need to cut out, using a pencil or marker. Measure the area twice -- it's easier to double-check your measurement than it is to replace the tub surround because of a wrong cut.
Place a 1/4--inch drill bit into the drill. Slowly drill holes in each of the corners of the area you marked.
Cut the tub surround with a jigsaw or handsaw. Start the saw blade in one of the holes you made. Cut through the plastic with smooth, fluid movements. Don't use coarse-toothed saws; they can chip the plastic tub surround.
Sand the cut edges of the plastic tub surround lightly, using a fine-grit sandpaper. Sanding will improve the appearance and safety of the cuts you made.