You can delete individual messages, conversations, or your entire chat history by following these steps. These steps apply to individual and group chats. Deleted messages are permanently deleted from your phone. Read this article for information on backing up chats that you wish to save.

To delete a single message from a conversation:

• Open the conversation or group chat.
• Scroll to the top of the conversation and tap [Edit].
• Tap on the message(s) you want to delete (a red check mark will appear).
• Tap [Delete] at bottom of screen.

To delete a conversation or group chat:

• Go to the Chats section.
• Tap the [Edit] button in the top left corner.
• The  icon will appear to the left of each chat.  Tap the  icon next to the chat you want to delete, and a [Delete] button will appear.  Tap to delete. 

Alternatively, you can:

• From the Chats screen, slide your finger across the chat row.  The [Delete] button will appear.
• Tap to delete.
• NOTE: If you delete a group chat, you will be removed from the group, and must be re-invited by the group admin. If you were the group admin, a new one will be randomly appointed. More information about group chats can be found here.

To delete your entire chat history:

• Go to the Chats section.
• Tap the [Edit] button in the top left corner.
• Tap the [Delete All] button in the top right corner.
• NOTE: This will delete all chats from the Chats screen, as well as exit you from all groups.

To clear all chat history, but continue to participate in groups:

• Go to WhatsApp > Settings.
• Scroll to the bottom.
• Tap [Clear All Conversations].
• NOTE: Using [Clear All Conversations] will not remove you from any groups.

Learn how to delete messages or chats on: Android | BlackBerry | Nokia | Windows Phone.

Cheers,
WhatsApp Support Team