Thumbnail Captions

Hello

I an trying to sort out the captions on a clients site and I know I have to edit nextgen-gallery/view/gallery-caption.php but when I go to plugin screen and edit and selected the correct plugin the above is not seen to edit?

I am trying to change the $image value to pull in the value alttext rather than the description field but cannot locate the required php page to do this?

Many Thanks

http://wordpress.org/plugins/nextgen-gallery/