You can only delete messages you sent yourself. There are two ways to do it:
Delete for me. Removes the message from your own view only. Everyone else in the chat still sees it.
Delete for everyone. Removes the message from view for everyone in the chat, straight away. It's worth knowing that a copy may still be kept for a limited time for safety and legal reasons โ for example, if the message had already been reported before you deleted it.
Deleting a message doesn't notify the other person with a special alert, but depending on how the chat displays it, they may see that a message was removed.
If you'd rather remove an entire conversation, or a story, see our Privacy Policy for how long different kinds of content are kept.