When Arnold is the currently selected renderer in 3ds Max, the Render Setup dialog will give access to Arnold settings.
These are global settings that control the behavior of Arnold rendering throughout the scene (there are also per-object settings, accessed via the Modify Panel).
To access the global render settings choose Rendering > Render Setup... or click on theicon. The dialog window below will be shown.
The first tab (Common) provides access to output drivers so that you can write the Arnold render out as EXR, PNG, JPEG, etc. The second tab (Arnold Renderer) provides access to the parameters that control render quality, lights, motion blur, etc. They are divided into groups. The fourth tab (AOV Settings) provides control over Arbitrary Output Variables (passes).