Open the Facebook Messenger app
Tap your profile picture
Tap Account settings or Privacy and safety
Tap Deactivate and delete or Account ownership and control
Tap Deactivation and deletion
Select Delete account
Follow the prompts to confirm
If needed, delete the Messenger app from your device
On iPhone, press and hold the app icon, then tap Remove App
On Android, press and hold the app icon, then tap Uninstall