Delete Google Contacts (if synced):
If your phone contacts are synced with Google Contacts, deleting them directly from contacts.google.com on a computer will sync the deletion to your phone and, consequently, to WhatsApp.
How to do it:
Go to contacts.google.com in your web browser.
Select the contact(s) you want to delete.
Click the "More actions" (three dots) icon at the top and select "Delete."
Confirm deletion.
Refresh WhatsApp Contacts:
After deleting contacts from your phone, manually refresh your WhatsApp contact list to ensure the changes take effect immediately.
How to Refresh:
Open WhatsApp.
Tap the New Chat icon whatsapp number list (usually a green circle with a speech bubble or pencil icon).
On Android: Tap the three vertical dots (Menu) in the top right corner. Select "Refresh".
On iPhone: This step is often not explicitly needed as iOS usually refreshes contacts automatically.
Block Contacts (Instead of Deleting):
If you want to stop receiving messages or calls from someone on WhatsApp but don't want to delete them from your phone's address book (e.g., a colleague, family member), you can block them.