AP1 form change name- which name

I'm just completing my AP1 form to change my name following marriage - I'm confused which name to put in section 6,7 and 15. Am I applying with my new name? If its all my old name then how is it known what I'm changing it to?! Might be a silly question it's just baffled me and I'd rather get it right!

Georgina - You are applying to register your new name so that's the name you need to state on the form.