Cancelling your subscription is easy.
Just navigate to your account page, click on "Subscriptions" and you will see a "Cancel" option. Click on that to cancel your subscription.
You will receive a confirmation email and your account will change from "Enabled" to "Stopped" under the subscription column.
NOTE: You will still have access to the plans up until the date when your subscription expires.
For instance, if your subscription expires on Feb 14 but you cancel on Feb 2, you will still have access up until Feb 14. You can see the status of your subscription under the "Active" column. In the image above you'll notice it still says "Active">"Yes" - even though the subscription is "Stopped". Once it expires, it will say "Active">"No".
However, you cannot cancel and receive any refund.