I need to replace the scratched film protector on my phone screen ( not the glass ) Before I attempt this ( as I have never done it before ) any how to advice?

You should get one designed for your phone specifically. I would suggest you check out You Tube for instalation instructions.

Most of the newer protectors are actually thin sheets of tempered glass and they go on much, much easier than the old plastic film protectors. I buy them on eBay for my iPhone for a couple of bucks apiece.