tModloader can be install via the Change Software tool. When selecting tModloader make sure to also run the installer.
Make sure to make a backup before installing tModloader.
Terraria guide
How To Install tModloader
Quickly set up tModLoader on your Terraria server with Kinetic Hosting! Use the Change Software tool, select tModLoader, and ensure you run the installer. Remember to create a backup beforehand to keep your data safe!