There's no simple method of doing this since utorrent is designed to take advantage of all ports. If you block the default ports used by utorrent, the user can easily change which ports are used and they'll have access again.
What is the expected service of the wifi router? Is it in a setting where it's used as public access or is it in a private setting for home or office?
Since you really can't block utorrent as far as I know, the best option if this is for home/office use is to find the offending computer and either uninstall the program or throttle their connection via QoS if the router has that option available.
If this is a public use situation, you could probably block the sites where people search for torrents to download. That's not going to stop it altogether but it could slow it down.