So if you want to delete a WhatsApp Contact follow these steps:
The contacts that you have in WhatsApp are directly loaded from the contacts in your phones address book - there is no way to directly delete them from within WhatsApp.
To delete a contact from the WhatsApp contact list, you will need to delete the contact from your phone's address book.
In order to find the WhatsApp contact in your phone's address book:
Find the contact in the Select contact page.
Tap on the contact.
Then tap on the name at the top.
On the Contact info page, go to [Menu button] > [View in address book].
From there you can find the option to delete the contact from your address book.
Then, refresh your WhatsApp contact list by opening WhatsApp > > [Menu button] > [Refresh]
If you still see the contact, it is likely that you are seeing the conversation on your Chats screen. Simply tap and hold on the contact and then select [Delete chat] to delete a chat.
And thats it!
If you have any other WhatsApp related issues have a look here -> Help! I have a problem with WhatsApp! Here are the solutions!