Can't update or uninstall built-in Whatsapp
You have to uninstall and reinstall latest version of WhatsApp. It will fix your issue.
Since your phone have built-in WhatsApp Application(system app) you can't normally uninstall your App.

Try to uninstall using Debloater which helps to remove a built-in App without root.

After uninstalling try to install a latest version of WhatsApp APK file from here

Source