To remove or delete the Blackberry WhatsApp chat conversations or history/archive, there are two ways :
1. Directly by deleting on every line of chat
2. From setting menu and delete all chat conversations / history.
The first way is to remove chat conversation of each line chat by placing the cursor directly to the chat line that you want to remove, and then immediately press the del button/keypad, then the chat conversation will disappear.
The second way is to delete all chat Conversations :
Go to the Setting menu
Scroll down the cursor and choose Advanced Settings
Select Delete Chat History and/or Delete Message History, then the warning will appear ask if you really want to delete or cancel, choose Delete.