Proration for plans and addons is accomplished in two parts:
The calculation of charges for unsubscribed items and unused time period of the current billing term.
The calculation of charges for the newly subscribed items for the remaining portion of the current billing period.
Upon upgrade/downgrade, the new subscription charges for the subsisting month would be charged on pro-rated basis and your credit card will be charged automatically. If payments for your account is made through other accepted payment methods, corresponding invoice for proration will be generated. Upon downgrade, you will be offered a refund for the payment made for the subsisting month in the form of credits credited to your account. These credits will be offset against the new Subscription Charges payable in the subsequent months.