Open WhatsApp
Go to the Chats tab
Open the chat with the number you want to delete
Tap the contact name or number at the top
Tap Edit or the three-dot menu
Select Delete Contact or View in Address Book
Delete the contact from your phone’s contacts
Return to WhatsApp
Refresh contacts if needed
If you want to remove the chat too, go back to the chat list
Long-press the chat
Tap Delete chat
Confirm deletion