You can delete your account from within WhatsApp.

WARNING! Deleting your account is an irreversible process, we cannot undo a deletion if you complete the process by accident.

Deleting your account will do the following:

• Delete your account from WhatsApp.
• Delete you from your friends' Select contact lists.
• Delete you from all WhatsApp groups.
• Erase your message history on your phone.
• Delete your WhatsApp service payment information

To delete your WhatsApp account:

1. Open WhatsApp.
2. Press the [Menu Button] > Settings > Account > [Delete My Account].
3. Enter your phone number in the full international format and tap [Delete My Account].

Please note that we cannot delete your account for you at this time.

Learn how to delete your account on: iPhone | BlackBerry | Nokia | Windows Phone.

Cheers,
WhatsApp Support Team