As a couple of others have mentioned it is no big deal. You must remove the inner frame (16 of these funny square head screws), pull out the rubber spline holding the screen in, cut a new piece of screen a couple of inches larger than the original, re-attach the screen with the spline, trim excess screen with a razor (carefully), replace the frame and admire your work! Note: you will need to remove the trim piece below the valance (3 screws) to remove the frame.

[Robert Wilson]

Thank you for this info. Saved me time!