When you order a plan upgrade, you will be credited for your current plan and charged for your new plan.
On upgrading your plan, overnight, a credit is generated for the unused portion of the old plan. Then a charge for the new plan is posted. The amount of the charge will be for a FULL period, rounded down in order to sync with your account’s monthly billing day.
Any credit on the account would then be applied, with the difference being charged to the credit card on the account.
to see a comparison list of plan features and prices.
For instructions on how to change the plan for your site, see this Knowledge Base article
* If the upgrade charge fails the account will go into past due status, and we will attempt to collect again on the normal past-due schedule.