Upgrade a plan / getting credit

I'm on a Standard Plan for $24 per month. I'm paying yearly and about 4 months in.
If I want to upgrade to a Professional Plan at $48 per month, do I get the remaining 8 months credited agains the price of the new upgraded plan?

At the moment, it looks like it's trying to debit the full price of a new plan and doesn't take into account the fact that I've already paid approx $288.