Licensed TrojanHunter users can easily update using TrojanHunter's LiveUpdate utility.
If you are using the trial version of TrojanHunter, use LiveUpdate after installation and then manually update after a few days (once a week or more is recommended).
License holders without an ongoing subscription please see http://www.misec.net/trojanhunter/updating/ for instructions on how to manually update to the latest ruleset.