To update your WordPress page’s Facebook link preview we must first understand where it comes from. The image, title, description, and site name that appears when a page link is posted on Facebook all originate from Facebook’s Open Graph. The Open Graph stores these properties for any link shared on the site. These Open Graph properties are read from your page’s open graph header tags:
og:title, og:description, og:image ect. To view the current open graph tags found on your page, you can enter your link at https://developers.facebook.com/tools/debug/. These properties are also cached, meaning they will not be updated immediately when you update your page’s Facebook Open Graph Tags. To force update the properties stored in the Open Graph for a given page, simply enter the link again in the Facebook Open Graph Debugger.
These fields can by updated using the Yoast SEO plugin, with instructions located here. You should now have all you need to update your WordPress page’s Facebook link preview!