Login to your Facebook app and start using the app. On the Home-screen of your App just follow the below steps:
Step 1: Tap on the App settings.
Step 2: Scroll down and tap Home Settings. You can also access these settings by tapping on your phone's lock screen.
Step 3: Tap Wallpaper, then tap to choose a group of photos (ex: Photos I've Taken, Photos of My Friends).
Each time you turn on your lock screen, you'll see a different Facebook photo from the group of photos you've selected. To turn off Home wallpaper, press and hold your phone's home screen, then choose a new wallpaper. Its more fun with Facebook.