updating from 3.1 to 3.2 is a major undertaking, not suggested.
updating from 3.1.2 to 3.1.12 is not that hard, just time consuming.
however, if you want to update to 3.2 then you need to get a new 3.2 style and use it. find one that is close to what you have and tweak it if needed.
what style are you using now with your 3.1 board.
I am available for custom work on a donation basis. Please send me a PM with your needs.
Premium phpBB 3.2 Styles