How to Install Replacement Windows

Adjust the unit by inserting shims under the sill and behind the side jambs until it is centered in the space and opens, closes, and locks smoothly. Measure the window diagonally from corner to corner; the measurements should be the same. When the window is square, screw it in place through the predrilled holes. To avoid bowing the frame, slip a shim behind the jamb at each screw, then screw through the shim. Trim the shims flush with a utility knife.