How to get new iCloud artwork?

Since the time that I first aquired a moive on iTunes, the artwork has changed (I see it via iTunes in the Cloud), and the new artwork is rather cooler than the original artwork. Without deleting the movie and redownloading it, how can I get the new artwork? I tried right-clicking on the movie and selecting "Get Album Artwork" but since it already has artwork, it won't download the new one. I even tried deleting the current artwork and trying again, and it still doesn't download anything. I don't want to have to delete the movie and redownload (over 3GB), so how do I get the new artwork that's attached to the movie in the cloud?