There is no straight way to delete your Facebook account permanently, if you think its enough and don?t want to use Facebook anymore. One way to deactivate your Facebook account is from Deactivate Account section from Account Section. This makes your account inaccessible to other Facebook users. But it is just like logging off. Once you log into account, it is once again accessible like nothing has happened.
At some point you would like to delete your account permanently for whatever may be the reason. If you need to deactivate permanently you have to search Facebook help for delete Facebook. Help can be accessed by the help text located at the footer of the Facebook page. There you will see submit your request here. From that link you can deactivate your Facebook account permanently. I guess it will give 15 days time until you log on to restore your account. If you don?t it will be deleted permanently.