update thumbnail in post

I have recently moved from using drupal to wordpress and as so adjusting.

I love the Hueman theme and can relate to page/ post areas but i am having problems with areas where i am not sure if it is a theme issue or a wordpress release issue.

I have cropped a thumbnail to show a different part of the image and using the ALXTabs the post picture does not update to the one I have cropped.

I have looked in forums etc for advice before posting.
Any advice would be greatly appreciated