When you share the website URL on Facebook, a preview snippet will appear with the title, description and image of your website.
This image can be uploaded via the Personal Website Builder > SEO > SEO Image.
After uploading a new image, you might also need to clear the Facebook cache that stores a cached version of the preview data. This can be done via https://developers.facebook.com/tools/debug/
Using the link, you can see how Facebook preview of your website will look like and you can clear the cached data so that Facebook crawlers can retrieve your latest uploaded image.
