I completed my 6th grade for Piano a few years back (thank god I don't have to do exams anymore). There are no specific number of marks awarded for each section of the exam. There aren't really any marks at all. Just either a tick if you can do something, or a tick if you can't. I suggest you focus most on your scales and your pieces... they're the main bit. As long as you can perform those solidly, you'll be set to go.
Also try and remember some info on each of your pieces. Just make some notes, and read it to yourself each today. I also find that if you write on a spare copy of your music, and then read off that, it helps you remember. Make sure you know the key signature, a little bit of info on the composer, what form the piece is in and what period its from and all the terms that are written on the music. Ask your teacher for what you should know.
Also.. I know sight reading and all that aural work is a part of it as well. I'm sure your teacher will spend a little bit of time each lesson going over that for you.. but don't stress too much.
Some examiners are really nice, and even if you stuff up your scales or pieces a bit, they just know you're nervous and ignore the little mistakes you make. But some are really strict and can be really harsh on their marking.. so you just gotta hope for the best.
Good luck with your exam! Just keep practicing everyday and I'm sure you will do fine.
