Hello @LisaD8358 ,
Regardless of whether you made the post via the Social Post tab at the top of the screen, or a campaign's specific Social Share function, you should be able to go in on the Facebook side and change or delete the image associated with it.
I went into your account to take a look at the social posts and they have been completed and are in done status. You will want to access them on your Facebook page to make any edits, as they can not be edited on Constant Contact. I do apologize for any inconvenience this may cause.