Click a button in wp-admin to force an Open Graph rescrape.
When you share a post/page on Facebook, it scrapes the url for the Open Graph Data to determine what image/video/content to display. Facebook caches to image for you so if you need to change it, the old image will still be displayed. Probably not what you want to do. You can manually go to the Facebook Debug Tool and click “Fetch new scrape information”, but this might be time consuming.
This plugin programatically forces a rescrape. Just click the button in wp-admin.