If it's torrent software then OpenDNS is unlikely to block it because most torrent software out there is P2P and does not go through a centralized internet service. There might be a website or something that is used to facilitate handshaking between clients, so you might be able to identify a domain or domains associated with it and block it.
You will more than likely need to rely on firewall logs, or perhaps wireshark, to identify where it's sending traffic and perhaps block it that way. If it identifies specific domains you can block those. Firewall logs or wireshark might also identify ports that can be blocked in the firewall, though some torrent software is pretty free to pick the ports it uses. Similarly you might also be able to block IP addresses, though since it's P2P software that might be ineffective.
If you are using Umbrella installing the agent on the computers might be of some use, as well as using one of the OpenDNS virtual machines. Of course that will still require you to identify any applicable domains, though the odds are low that any DNS blocking service will be able to block the software from connecting if it's already installed on the computer.
The big question is why are these students able to install the software in the first place? If they are school property they should not be logging into the computers with administrator access. If they are, then it doesn't matter what you do with OpenDNS or anything else because there are a myriad of ways that they can block or change anything that you configure. If they are using personally owned devices to connect to the internet using your network then you might need to turn that capability off until you find a way to block this activity.
