There are too many old contacts i need to get rid off. But i don't know how.

How can i do this?

just block them.

You would have to delete the contacts from your contact list.
From WhatsApp:

The contacts that you see in WhatsApp come from your address book. There is no way to directly edit the Select contact screen.
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.

https://www.whatsapp.com/faq/en/android/23179277

Cheers.

Karmanaut:
You would have to delete the contacts from your contact list.
From WhatsApp:

https://www.whatsapp.com/faq/en/android/23179277

Cheers.

thanks, it worked!