From the Client Area, click Domains:
Then click the small arrow next to your domain (Step 1) and select "Auto renewal status" (Step 2):
On this page, you can disable or enable domain auto renewal:
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.