UI Manager

In this place, you can adjust all game UI (inventory, game pause, character's UI, multiplayer Lobby, etc.)

Open it by pressing [Edit -> USK Projects Settings -> UI Manager] and then open* the prefab to customize UI.

*if you're using a Unity version up to 2018.3, you should place the prefab in a scene, change UI, then apply changes.

UI manager has 3 main tabs and clear prefab structure: