Facebook offers two options to its users: Deactivate and Delete. If you plan on temporarily deactivating your account with the intention of getting it back after some time, then all you have to do is to deactivate your account. However, if you wish to permanently delete your Facebook account, it should be noted that you will not be able to access your account again.
To permanently delete your Facebook account, just go to facebook.com/help/www/359046244166395, choose “How do I permanently delete my account?”, click “let us know”, log in to your account, and then you will see a message stating: “If you do not think you will use Facebook again and would like your account deleted, we can take care of this for you. Keep in mind that you will not be able to reactivate your account or retrieve any of the content or information you have added. If you would still like your account deleted, click "Delete My Account".