Sharing a page to Facebook pulls the following information for display:
Title - by default, this will be the defined title of the page that appears in your browser, i.e. “Home - The XYZ Foundation”
Description - by default, Facebook will display the first paragraph-level language on the page.
Image
You can set a default sharing image for all of your WordPress pages/posts by logging in to the WordPress admin interface and going to SEO > Facebook > Default settings and uploading an image
If you do not set a default here, Facebook will display the first image that is displayed on the page and is larger than 200x200px. If the first image is too small, Facebook will display the next image.
If you want a preview of what will display to these services when you share a page, you can use Facebook’s handy Object Debugger
Enter the URL you plan to share and click Show existing scrape information. On the resulting page, scroll down to the Link Preview:
This will show you what would appear on Facebook if you shared this URL right now.
Updating Social Sharing with Yoast SEO
If you don’t like what you see in the Object Debugger, it’s easy to change using the Yoast SEO plugin that we’ve installed on your site. You can define a new title, description, and/or image for the page, then tell Facebook to “refresh” to get this new information for sharing.
To change this information for a page, in the WordPress Administrator Interface, go to Pages > All Pages and Edit the page you wish to update. On the Edit page, scroll down to the Yoast SEO section and click the sharing icon. Here, you can enter your own Title, Description, and Image.
If these are blank, it means that the page is currently using the default sharing properties. Make your updates, scroll back up and click Update to save your changes.
Refreshing Facebook Sharing
Facebook very kindly lets you request an update to the sharing information for any URL using the Object Debugger noted above.
To request a refresh, go to the Object Debugger and enter the URL for the page you just updated. Click Fetch new scrape information. Scroll down to the Link Preview section to see your updated sharing information.