If you would like to permanently delete your Facebook account, follow these steps:
1. Login to that account you would like to delete.
2. Click the following link which will take you to the official account deletion page.
The link is:
https://www.facebook.com/help/delete_account
After clicking this link, you will be required to confirm your action and enter your password and then your account will be deleted permanently after two weeks.
If you have lost your loved one you can request the account to be deleted or just memorized by reading the following from Facebook help center.
To request the removal of your loved ones account, read this help:
https://www.facebook.com/help/www/265593773453448
To memorize the account of your loved ones, click the below link to request:
https://www.facebook.com/help/contact/305593649477238