From the Client Area, click Domains:
Next click anywhere in the row of the domain you wish to manage (ie on the "Active" text):
On this page, click the "Auto Renew" link in the left navigation bar. Then you will be able to see the current auto-renewal status, and enable or disable it as per your preference:
Please note that domains have auto-renew enabled by default. If you don't wish to renew your domain, you must disable auto renew manually.
Note: If you have several domains, and you'd like to update the bulk renewal status on all of them, you can also use the "Bulk changes" option
Please open a support ticket if you need any further assistance.