Once a domain is registered, it cannot be manually cancelled like a hosting service. If you no longer want a domain, disable autorenewal and wait for the domain to expire.
Before you start:
Step 1 - Log into your Client Area and click on Domains.
Step 2 - Confirm your domain's Auto Renew status by reviewing the tick or cross next to 'Auto Renew'.
The green padlock indicates whether your website is protected by an SSL Certificate and is not related to auto renewal status. For more information on the SSL Status, use this external tool.
Step 3 - Click on Auto Renew or anywhere on the domain row to open the domain options page.
Note: Clicking directly on the domain will bring you to the website instead.
Step 4 - Navigate to the Auto Renew tab to review the current Auto Renewal Status. To disable auto renewal, click the 'Disable Auto Renew' button.
To update the auto renewal status of multiple domains, navigate to the Domains page and select the domains you wish to update.
Then click on More >> Auto Renewal Status in the top bar.
This will bring you to a page where you can mass update the status for all the selected domains.