Sorry to be the bearer of bad news but if you want you should politely ask them to take it down, and then offer your own. People are obviously interested, and I'd love one for my laptop, I'd just like to give the credit where its due.
Thanks for showing me this, I'll be sure to take care of it! I appreciate the interest but I can't help but have mixed feelings about selling my art. I always get a 'sell fanart at your own risk' vibe from these kinds of sites, and I've heard Disney doesn't take too kindly to copyright infringement. Of course, I feel guilty for being so reluctant because I want to make nice things for people like you!