Remove the screen frame from the window
Lay the frame on a flat surface
Pry out the old spline using a flat tool
Remove the old screening material
Cut the new screen mesh larger than the frame
Place the new mesh over the frame
Press the mesh into the spline groove
Roll the spline into the groove with a spline roller
Keep the mesh taut while rolling
Trim the excess screen with a utility knife
Reinstall the screen frame in the window