Before you go on to delete your Facebook account permanently, you should download your Facebook data by following these steps.
1) Go to Settings from the drop-down arrow on the top right corner of the screen.
2) Select General Settings and click “Download a copy.” Click “Start My Archive”. You might be asked to enter your password. Once entered, you will be asked to click “start my archive” again.
3) Facebook will then gather the data and send the download link to your email
4) Upon clicking the link, you will be redirected to Facebook where you can find “Download Archive”.
5) Click the green button, and your data will be downloaded to your system.
You have downloaded your backup. Now proceed to delete your Facebook account by clicking Delete My Account page on Facebook.
After 90 days of deleting, your account, history and every information will be removed from Facebook's database and servers.