You can make sure you're always using the latest version of the Facebook app by turning on automatic updates. To turn auto-updates on or off:
- Open the Play Store app. 
- Tap the top-left corner > Settings. 
- Tap Auto-update apps and choose one of the options: 
- Do not auto-update apps. 
- Auto-update apps over any network. Data charges may apply. 
- Auto-update apps over Wi-Fi only. 
