Paying off phone and upgrading early

[Bingo99]

hello, I was looking advice on what would be the best option in terms of upgrading my daughters phone early. I took out a contract in November last year via mobile phones direct and there is around £700 remaining which I was planning on paying off early via o2 directly. The best deal for the new contract is via mobile phones direct but I want her to keep the same number, how does this work if I pay the previous contract off via o2 and use mobile phones direct for a new contract? Sorry if this sounds like a really silly query, I have a brain injury which makes these things very difficult to understand. 

[MI5]

@Bingo99 

You need to do an upgrade with Mobile phones Direct and they will bill you for the money owed from the old contract and carry over the phone number to the new contract.