How to change link preview image for article?

[RaiinbowEyes]

Greetings!

So I'm having an issue that I hope someone can help me with. I have an article that I've linked to a tab in my nav bar, and just bought a redirect for people to share, since it's an information page. However when I link it, like on Facebook, the preview image that shows up is not one that I want. There are many photos in the article (42 images, actually) and it uses the 9th image.
Sometime it will let me select between the 9th, 11th, and 33rd images, but that's it. And of course it doesn't help when other people share the URL, that it automatically chooses the 9th image which is not very appealing. None of these images are attached to the article, they're all uploaded on the server.

To clarify, I'm not talking about the article preview image on vbulletin (no one sees that one so it's not an issue). I'm talking about the preview image that comes up when I link it on social media. Does anyone know how to change this? I'm using vB4.2.2 if that makes a difference.