How to edit Facebook Open Graph Image
When sharing your website on social media sites, such as Facebook, a small description and image are usually accompanied.
This image and text is based on your Page Settings. If you would like to edit this click the Pages link on the top menu or the Plus + button on the page tabs bar to open the Pages & Navigation window.
Use the fields highlighted above to edit the information displayed on Facebook.
When uploading your "Page Image" use images that are at least 1200 x 630 pixels for the best display on high resolution devices. At the minimum, you should use images that are 600 x 315 pixels to display link page posts with larger images. Images can be up to 8MB in size.
After adding your Page Title, URL and Image you can also click on the SEO tab to edit your Page Description:
After saving your changes, be sure to publish your site.
You can test your new data with Facebook's Sharing Debugger.