thumbnail update doesn't doesn't post to gallery

I have a site using 3.32 WordPress and NextGen Gallery With a Headway theme. In the past I have had no problem updating the thumbnails on the “manage Gallery ” page, but now, after I click “update” and the thumbnail shows that it has been updated, it doesn’t show on the gallery page. I always hit “save changes” and on another forum someone had said to clear the cache and I am not sure of how to do that- I tried clearing a cache under “image settings” but not sure that was how to do it and it didn’t work either.

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