It is likely a new plan will be better than any existing one (i.e. cost/data).
As long as your current dataplan is out of contract then simply order a new one and cancel the existing once activated.
Changing a number short of a court order isn't easy.
...but just to note than 2 numbers cannot use the same dataplan if that's what you're asking. (Each number must have its own active dataplan)
I am just another Sky customer and my views are my own even if you don't like the answers
