WARNING! If you have UOSteam installed in your UO folder, you should make a copy of your UO folder and install Orion into this copy. Otherwise you might lose all your UOSteam settings.
Download Orion Launcher
1. Download OrionUO Launcher and install it.
2. Open OrionUO Launcher and define the path to Ultima Online root folder.
3. Go to Update tab and click on "apply updates" button.
4. Open Client Configurator and specify the client version that is used on your server.
5. Start OrionUO.
Video guide for Orion Launcher