[Plugin: NextGEN Gallery] Cannot change preview image

I am using the nextgen gallery on this site: http://www.carmensediblecreations.com/gallery/

My client wants to update/change which images are being used as the preview image… She tried it.. didnt work.. I tried it.. didnt work..

Help?

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/