PlusNet contract 60gb - help on contract options

I've just set up a PlusNet contract with 60gb usage per month and had hoped it would be by far enough but very quickly its starting to seem it may not be enough and so I may have to pay extra. I think streaming video is going to be the big usage killer.
I've only had the package a couple of days but I'm thinking if I were to swap contracts for an unlimited deal, say with O2, it may be easier to state unhappiness now rather than mid contract.

Can anyone give any help on PlusNet contracts and if they have a 'happiness' 30 day period or anything? Havent been able to find anything on the subject. Many thanks in advance.