How do I cancel going to Uni???

Suggestion - defer your offer for a year rather than just cancelling it.

This way you still have Uni as an option if the job doesn't work out, or you simply change your mind. You have nothing to lose by deferring - you can still cancel it at any point up to Sept 2017.

Thank you I appreciate that, I know I might sound stupid by asking but how exactly do I defer the offer?

Contact your universities and ask them. And it's much better to do it now than on Results Day.