Things You'll Need
Screen section that is larger than the damaged screen section
Since window screens must be thin enough to allow air to pass through while preventing insects, dust, and debris from entering your home, they can be prone to damage. If a screen on your home is damaged you can replace it yourself by purchasing new screen at a hardware store and fitting it to the screen's frame.
Measure the dimensions of the damaged screen section using a measuring tape and purchase a new screen section that is at least as large in both length and width as the damaged screen.
Remove the damaged screen panel from the window frame. The process of removing the screen pane will vary based on the window. Usually the window must be raised and the screen panel must be unscrewed, unclasped or popped out of place.
Remove the screen from the screen frame by pulling out the spline cord that keeps it in place (you can get the cord started with a screwdriver) and tugging the screen out once the spline has been removed.
Lay the new screen section on top of a large piece of cardboard placed on a hard surface, such as the floor of a garage.
Lay the damaged screen section on top of the new screen section.
Align a straight edge, such as a T square, with the edge of the old piece of screen to provide a guide for your cut.
Use a sharp utility knife to cut the new screen along the straight edge. Only use enough pressure to cut the screen. The knife may sink into the cardboard a little bit, but don't press down so hard that you cut all the way through to the floor.
Continue cutting with the utility knife and straight edge until you have a rectangle of the new screen that is roughly the same size as the damaged screen.
If the new screen is cut slightly larger than the old screen it is not a problem, but don't cut the new screen smaller than the old screen. If you want to cut away a damaged portion of a screen in an attempt to patch the screen, you should still remove the screen from the window and set it flat before cutting. Never attempt to cut a screen that is still in a window as it can stretch and damage the screen even more.