how do I remove tape for insider plastic?

Answer 1

try isopropyl alcohol (i.e. rubbing alcohol), first
Use lots of paper towells to rub off the softened gum.

Answer 2

I'm guessing you're referring to the plastic sheets you can tape over windows to keep out drafts or prevent heat loss in the winter. Any solvent that will dissolve the adhesive base without destroying the edge of the window will work. Try it in an inconspicuous spot first, use it sparingly and don't rub vigorously.

turpentine, varsol, alcohol (methanol), acetone (nail polish remover)

Final word: DON'T mix them, if one doesn't work, let it thoroughly dry first before you try another.