Login to customer portal, view your service under services tab, and on same row with service there is "view details" button - you can request cancellation under this button.
You can then choose immediate or at the end of payment cycle. Please note that this does not cancel your Paypal subscription if you have any, you need to cancel that separately.
The actual cancellation of service does not happen immediately, but after a while after the chosen cancellation time. Cancellations happens usually within 1-2 days.
