Do I pay full price when I upgrade my plan?
In this article, you will find if you pay the full price when you upgrade your plan
No. You don't pay the full price of the new plan when you upgrade. Indeed, because you already paid the smaller plan, you will only pay the difference prorated when you upgrade to a bigger plan.
The difference will be credited on your account and deducted from the next invoice(s). If you upgrade your plan, you'll see the credit on the billing page: