Refresh Facebook open graph image for your site
Facebook has a schedule of purging its cache, but if you need to get rid of an old image sooner, it’s easy (although not obvious) to do it. We assume of course that both images, your old and your new one, have the same name and are served in the same URL.
First of all, make sure you purge your own cache, if you use Cloudflare or some similar service to cache your media. Check if your new image now appears in your browser without problems, then go to https://developers.facebook.com/tools/debug/
Enter the URL of your new image, e.g. https://static.fbcdn.net/mynewimage.png and click the Debug button.
If Facebook shows instead your old image, press the “Scrape Again”. You may even need to hit F5 in case that your browser uses its own cache to show the previous version of your image.
Now Facebook should be updated with your new image. At the Sharing Debugger above enter the URL of your site instead of that of your image. You should see that Facebook now uses your new image sharing an address of your site. Note that your image should be at least 200 x 200 px for Facebook to use it.