You can override the out of the box OG images by adding the following code to the HEAD section of your page layout:
<!-- Facebook -->
<meta property="og:image" content="https://peoplevine.blob.core.windows.net/media/72/powered-by-pv-og.jpg" />
<meta property="og:image:type" content="image/jpeg" />
<meta property="og:image:width" content="1200" />
<meta property="og:image:height" content="628" />
Replace the content link in the code to change the image.
To have Facebook refresh the image that was pulled, use the Facebook Scraper to fetch for a new image:
Insert the URL to your homepage
Click the "Debug" button
Click "Scrape Again" 2-3 times.
If the image is not showing, hit "Debug" again and then "Scrape Again" 2 more time
If the image won't refresh, the code was not place in the correct section or you can try clearing your browser cache and starting over.