You can cancel your subscription at any time by visiting your ReadablePro account management page, and clicking the "Cancel Subscription" link. We ask for a little feedback about why you are cancelling, but that is completely optional.
Alternatively, you can drop us an email if that's easier - please confirm the email address you used to sign up, and when you would like the subscription to end.
When you cancel your subscription, you don't lose any time you've already paid for. Cancellation just stops any further payments being taken in future.