The way I changed the order of the posts in the slider was simply by changing the dates and times of the posts so that the one I wanted to show first had the latest time.
AdmiralRob, I got it to work by using the link on that page. When it brings me to the Instagram page that requests, authorization, you’ll see this in the last part of the URL:
&redirect_uri=http://davidmregister.com/instagram-widget-for-wordpress/&response_type=code
Change the last word from “code” to “token” and hit Enter. From there, click the “Authorize” button. As of today, that’s what I had to do to get it to work.