People often confuse between deleting Facebook account and deactivating Facebook account.
Deleting your Facebook Account means completely removing everything in your account permanently and forever while Deactivating Facebook, means just hiding your account so that others wont see anything about you but you can activate it again any time upon login to your Facebook account.
Read Also: Temporally deactivate Facebook account
Before you completely delete your Facebook account you are advised to do the following.
Now if you are ready to completely delete your Facebook account, login to the account which you would like to delete and then click the following button which will take you to the official Facebook help page for deleting your account, where you will be asked to confirm that you want to delete your account and complete some security questions such as confirming your password.
You can not delete your account if you can not login to that account.
For your account to be deleted permanently, after finishing this step, do not login again for two weeks because if you login again within those two weeks your account will be reactivated.