Subscriptions can be canceled (or re-activated) at anytime on your subscription management page located here. It is your responsibility to cancel your subscription from this page. When you cancel your subscription you will still be able to utilize the services you have paid for until the end of your current billing period.
Example: if your last subscription payment was on March 1st and you canceled on March 19th your subscription will remain active until April 1st (since on March 1st you paid for access from March 1st - March 31st). On April 1st your subscription would automatically cancel.