How to reuse any domain names on new accounts?

On Clientarea said:

Domains on closed accounts cannot be registered again. To reuse any domain names on new accounts, you need to delete them from the account first.

So, what if I register domain, then how to delete the domain from the account?

If the account is still active, you need to go into the control panel and delete any subdomains, addon domains and parked domains you want to use again. If you already closed the account, you could try to reactivate the account, delete the domains and then close the account.