If you need to change your card information, or wish to cancel your subscription, you can do that any time right from this page. Click on the portrait oval in the upper-right and choose "Settings". On the next page select "Billing info" (also in the upper-right). If you paid using a credit card, you can change your card info or cancel from here. If you used PayPal, you have the option to cancel.
If you do decide to cancel, remember you'll still have access to the free content and forum for as long as you'd like!