Cancel anytime. Simply login and go to Settings > Account > Unsubscribe.
Upon canceling your annual subscription the balance of the plan will be prorated monthly, based on the date of cancellation. A refund for the remaining months will be offered and credited to the card on file.
Refunds for the balance of monthly or daily subscriptions will not be offered. In this case, the billing cycle will simply stop and no further payments will be processed.