Download the latest version of Mods for HESK along with any language packs.
The latest version of HESK is 3.1.1, but Mods for HESK only supports HESK 2.8.4.
There are currently no plans to support HESK 3.1.1.
Answer this simple question to retrieve installation information.
http://<path to your helpdesk>/install, click "Install / Upgrade Mods for HESK", and then follow the on-screen instructions.