heat the outside of the glass with a heat gun (hair dryer will do it but it's slow) to soften the adhesive, rather than the film itself. Lift an edge and it should come off in one go - easier with two sets of hands so that someone else can keep the heat on the glass. Go slow and pull the film right back on itself, rather than 90 degrees out from the glass.
Use d-limonene (citrus solvent) to remove any residue and clean glass well afterwards. You can use a goo remover like Oomph (d-limonene is the active ingredient) or acetone/goof-off at a pinch, but the limonene will basically turn it to jelly if you let it dwell, so you can just glide a razor blade through it (plastic razor blade won't hurt the demisters) and won't affect any surrounding plastics (which acetone most likely will)