How to Replace a Window
Pry out the old spline with an awl or a narrow-tipped screwdriver. Throw it away— spline gets hard and brittle as it ages and shouldn’t be reused.
Lay the new screen material over the frame. It should overlap the frame by about 1 to 2 inches around the entire perimeter.. Cut each corner at a 45-degree angle just slightly beyond the spline groove. The cuts keep the screen from bunching in the corners.
Using the convex (rounded edge) side of the screen rolling tool, press the screen material into the groove in the frame.
Begin installing the new spline at a corner. Using the convex (grooved edge) side of the screen rolling tool to push the spline into the groove. Continue around the frame. If wrinkles or bulges appear, remove the spline and reroll. Small wrinkles should tighten up as you get back to the starting corner.
Trim excess screen material using a utility knife with a new sharp blade. A dull blade will pull the material, not cut it. Cut with the blade on top of the spline and pointed toward the outside of the frame.