Before you delete your account permanently be sure that’s what you want to do, because once you delete it you won’t be able to retrieve it.
If you are not sure that you will never use that account again then go ahead and permanently delete your account. Once you delete it, you’ll not be able to reactivate your account or retrieve any of the content or or information you have added.
1> Go to http://www.facebook.com/help/contact.php?show_form=delete_account ,
2> Click on SUBMIT only if you are sure you want to delete the account.
3> Once you click on Submit, you’ll be taken to a page, where upon clicking OKAY your account will be permanently deleted forever.
You’ll be given a chance to reactivate it by logging into your account within next 14 days after deleting the account. Once you login you’ll be given the option to cancel your request. You can rethink about your decision.