@Gemmapollard
You can do it here (further down the page):
https://www.sky.com/help/articles/sky-mobile-upgrade
If you don't want a new sim then make sure you select the "I do not need a new plan/sim" option.
If you are struggling with this then give Sky a call on the free 150 number to do it.
If sending a phone back to Sky then make sure you get and keep proof of delivery.
__________________________________________________________________________________________
If someone has helped you then please click on the LIKES button in their post.
If you need help please provide as much information as you can
