Within the Domain Names section, click Manage Domain Auto Renewal, just below the Renew Domains link.
The Domain Cancellation page will show list of domain names registered within this account.
For the domain you wish to cancel / allow to expire, click the relevant box alongside.
Click Next Step.
Click Confirm Domain Cancellation.
The Domain Cancellation page will confirm the domains you have chosen to allow to expire and the date they are due to expire.
Please note: Once you have followed the above cancellation procedure you will not be sent any more reminders about the domains. However, if you do change your mind you can still renew them via the Domain Renewal option within the Control Panel.