Hi!
What error do you get when trying to update WhatsApp? Or do you not know how to update it?
If you don't know how, click the search icon on the taskbar > search for Microsoft Store > click Library > Check for updates. The MS Store will update all available apps, including WhatsApp.
If you are referring to WhatsApp Web, or if you installed WhatsApp Web as an app via your browser, it cannot be updated like a standard app.