Are you in a minimum term for your current contract? You'll need to factor this in to any decision making as if you are, it may be best to continue paying monthly rather than have the early termination fee in one go.
Assuming you're not (or you are and you're happy to pay the termination fee), contact EE customer services and cancel your contract. Be clear to them you want them to move the service to prepaid rather than disconnect your number.
The other alternative (if you want to switch in less than 30 days) is buy a PAYT sim from an alternative network and then generate your PAC from EE and port it over.
However as you mention you're already overseas, plan A (contacting EE) may be be the best way forward.
Out of interest, where have you moved to?
