Excuse me if I sound stupid, I am new to pay monthly 
My o2 18 month contract will be up within a matter of weeks, and I have seen a much better tariff on Orange that would suit me better, so how do I go about cancelling this o2 contract when it's up? Is it just by phone? If so, anyone know what the number is?
I ordered it online originally, not in a store, if that makes a difference?

My o2 18 month contract will be up within a matter of weeks, and I have seen a much better tariff on Orange that would suit me better, so how do I go about cancelling this o2 contract when it's up? Is it just by phone? If so, anyone know what the number is?

I ordered it online originally, not in a store, if that makes a difference?