How to update image of link?

I changed the image in my form however when I send people the link to register in facebook etc the old picture/thumbnail pops up.  How do I change that.  I've attached a copy of the link below.

https://secure.jotform.us/TrinityXpress/MarketingMaze

The form embedded properly on my website, I would just like the thumbnail to reflect the same picture that is actually in the form. 

Thanks

Marlena

marlena@trinityxpressions.com

Hi Marlene,

This is how the form appeared to my end when I attempt to post it on my Facebook wall:

The image is correct based on your form image settings. However, if you want to change it, then just simply edit the form in the form builder, click the image and re-configure it. Or, change the image URL directly in the toolbar:

Please get back to us if you need further assistance.

Thanks