Delete Account in WHM
From Lunarpages Web Hosting Wiki
This is how you would delete an account using Web Host Manager (WHM). This way you can get rid of any accounts you may not wish to have, or you are no longer using.
The first thing you would need to do is login to WHM. From the front page, click on "Account Functions" and then click "Terminate an Account". Now, you are on the Terminate an Account page:
Locate the account you wish to delete.
You can also select the account by clicking on its associated user name. To delete the account, hit the "Terminate" button. Having done so, you have now successfully deleted the account in question from your WHM install for your dedicated hosting plan.