You can change plans at any time. Any amount due is calculated by crediting you the unused duration on the current plan and deducting the remaining duration on the new plan.
Any prorated credit will be used to satisfy future billings.
When the change is made, a new billing schedule starts on the date of the change.
The current billing schedule is maintained.
If you choose to cancel your subscription, your account will revert to a free account at the end of the current billing period. No refunds are given.