Uninstall Facebook Messenger

Facebook
Messenger is one of the most popular messaging apps with billion users.
Facebook Messenger is now a separate service from Facebook on mobile
devices. Facebook Messenger is mobile app used as chat program. You can
only deactivate Messenger if you previously deactivated your Facebook
account. You can delete messages, conversations and photos from your
inbox. If you
want to remove yourself from Facebook chat completely, you’ll have to Delete your Facebook Account as well.
 

Uninstall Facebook Messenger on Android

    Open Messenger
    Tap your profile picture in the top left corner > Privacy & Terms > Deactivate Messenger
    Enter your password and tap Continue
    Tap Deactivate

Uninstall Facebook Messenger On iPhone        

Locate Facebook Messenger on your device
Tap and hold the Messenger app icon
Tap X (top-left corner of the Messenger app icon)
a pop-up will open Tap Delete

To Delete a Message or Photo:

    Open the conversation
    Tap and hold the message or photo you’d like to delete until a menu at the bottom pops up
    Tap Delete at the bottom

To Delete a Conversation on iPhone and iPad:

    View your conversations from Home
    Press and hold the conversation you want to delete
    Tap Delete Conversation

Delete Facebook Chat on Computer

Open Facebook visit this link https://www.facebook.com/
Click the Messages icon at the top right of the screen
Tap on the message you want to delete
Click the gear icon on top right hand side
Select Delete Conversation from that drop-down menu
Confirm to Delete This Entire Conversation.