If you ever upgrade your subscription, the difference of amount will be prorated during the time that remains on your current subscription and you will be charged the price of the new subscription in full only at the start of the next period.

You cannot have two different subscriptions active at the same time so you cannot get charged for both subscriptions if you ever upgrade, The system will automatically upgrade your subscription and you will pay for the difference in price that is calculated for the rest of your current subscription (for example, on a monthly subscription, if you have 3 days left, the payment will be prorated to the new upgraded one for 3 days only before being charged in full for the next month).

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