Facebook does not make it easy to customize the previews sent when sharing content. The biggest hurdle is that they save versions of websites and use old information at times.
But there is a way to fix it.
Facebook URL Debugger
Facebook provides a tool to manually test and reset information used for sharing.
Simply go to this address:
Then type in the full url that you want to reset.It should offer you a preview of the newly scanned site and tell you what it will use from now on for that url.