I have written some documentation and examples for using UGameUserSettings. This class is a facility for providing graphics options in your game via a graphical interface (such as fullscreen/windowed option, changeable scalability settings, etc). As of this writing it’s not exposed to Blueprint but it is simple enough to write a blueprint library class to expose it and the FQualityLevels struct it contains.
You can find it on the wiki. https://wiki.unrealengine.com/Game_User_Settings