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If you are in agreement and are not due an upgrade with a new subsidised phone, your options are :
Pay off what remains of the contract with a 2% discount and minus any VAT.
Purchase the new phone at your own expense. This option will enable you to change to a SIM only contract when you current contact ends and work out the cheapest option.
The other alternative is to take out a second contract with a new number and cancel your present contract when it reaches the end of the minimum term but this will mean paying for two contracts.
When is your upgrade date ? I ask because you could speak to Vodafone customer service to see if you can pay the remainder off and upgrade.
Or perhaps sell your current phone and use the funds to help pay for another. You could have it unlocked which can increase its street value.
Highstreet Shops such as c.e.x sell traded in / unwanted upgrade phones.