If you’re on an eligible Upgrade Anytime plan, you can upgrade from day 15 of your new plan and up to 45 days before it ends. There may be an upgrade fee to pay depending on where you are in your contract but you can upgrade every two weeks if you want - you just need to swap your old phone and sign up to a new 24-month plan.
in the first six months of your plan there's a £200 - 600 upgrade fee depending on what device you have
between six and 12 months into your plan there's a £50 - £300 upgrade fee depending on what device you have
after 12 months there is no upgrade fee
if you're in the last 45 days before your plan ends, you can upgrade as normal with no upgrade fee and you can keep your old phone