You may cancel your paid plan at any time.
To cancel your subscription, follow these steps:
Account>subscription and usage>downgrade
On the pricing table select the 'Downgrade' option on the Basic plan.
Cancellation of the paid subscription will take effect at the end of the current billing period. Up to the end of the current billing period, access to the quotas and features of the paid plan will remain in place. At the renewal date you will be switched to a Basic user plan. You will be subject to the quotas and features of the reduced plan.