You can 'Refresh' in Skins and Themes which add the latest skins to the 'Updates' feature but doesn't update Skins and Themes (Why, I don't know). Or you can choose View/Refresh Library Database which updates the whole lot but takes ages.
If anyone knows a better way let me know - its currently quicker to see new stuff on the web site than mess with Skins and Themes. I know its there in updates but that's not the point! >