Diamond Shield removal is a challenge.
Use a steamer to progressively loosen a working section ahead of a small, plastic, putty knife
Use a specific body shop, hard plastic(?) tool to remove the film. Being careful to avoid cutting into the paint.
You can use sandpaper to re-sharpen the leading edge of the tool,
Peel the entire Diamond Shield in one continuous sheet, if possible.
Try to maintain grip of the already-peeled plastic. Helps avoid having to continually scrape a glued-on edge.
Use something like "GOO GONE" Adhesive & Glue Remover to remove remaining patches of cured, stuck-on glue.