Changing the main profile picture in a gallery?

I can't seem to find a link to change a specific picture to the main profile picture of a TV show gallery?

For this case, I would like to change the profile image of this show: Frankenstein Code. They've changed the name of the show to 'Lookinglass' and I've uploaded an updated teaser poster showing the new title, but I can't change the profile image to reflect it. Help?