upgrade in the middle of a prepaid year

Hello,

I am considering of making a one-year prepayment. But what happens if I later decide to upgrade to a bigger plan? Will I be paying the difference of the discounted smaller plan and the normal larger plan monthy? Or do I pay the difference for the remaining term upfront? Can I get a discount on the upgraded plan somehow?

Let's say I have a one-year payment for a 512 node, of which 6 months have already expired. I want to upgrade to 1024. What happens?

thanks