To rescreen a window frame, remove the frame from the window to a flat work surface, pry out the old spline (the foam strip that steadies the screen), press the new screen into the groove and then press the new spline into place. This requires a screen that matches others in the home, a flathead screwdriver, a cutting tool, a spline roll and a spline rolling tool.
Once the window frame is removed to a work surface, pry the old spline out with a flat-head screwdriver, then remove the screen by hand. Stretch the screen material over the opening in the frame, and make sure there is ample overlap on all sides. If there is a lot of excess, trim down the screen material with scissors if using fiberglass or cloth screening or with a utility knife if using aluminum screening. Use the convex end of the spline roller to press the screen into the groove in the frame, then use the concave end of the spline roller to press the new spline into place. Use a utility knife to trim the spline. Finally, cut away any excess screen material until it is flush with the frame, and re-mount the frame.