After you remove the film, the glue will likely remain stuck to the glass, so here comes the messy part.
With some solvent, soften the glue and wipe it off with paper towels.
I started with OOPS, but that was not fast enough so I got some paint thinner.
I found out that if you cover the screen with paper towels and then soak them in paint thinner you can let it sit longer and dissolve the adhesive without running and evaporating.
Scrape off the soft glue with a piece of plastic or wood.
Be careful not to get paint thinner on the plastic frame, because it will dissolve it.