How do I install if my roof shingles are nailed down?

If your roof shingles or tiles are glued/nailed down at the roof edge, do not disturb the shingles, you can bend the mesh up or down in the back while retaining between a 5 and 25 degree forward slant (positive slope) on our gutter guard. Then you would screw the back mesh into the fascia, thus not having to slide it under the shingles. Once installed and ensuring you have the front edge of our gutter guard laying flat on the front edge of your gutter, then you should achieve optimal performance.