You can’t delete your Habbo Hotel account. Habbo is pretty unclear about when -at all- your account will be deleted. From their help pages:
We do not delete accounts at request. If you no longer wish to use an account you can take all your furni off of it, delete all rooms and spend all credits, the account will then be removed the next time that Sulake clear out unused names.
(Who the heck is Sulake?)