Up. It is a terrible design, set at a single height above the seat, which means it fits only a limited range of human, since everyone's arm is different proportionally to the length of their torso, and everyone's torsos are different lengths anyway.
For me, this means it sits about two and a half inches above comfortable, and it doesn't matter where I adjust the seat, because the butt-to-elbow distance remains constant (and yes, I do know the difference... butt goes in seat, elbow on armrest!)
I plan to delete, finding a nice substitute would be nice but I've gotten used to not having one, delete would be fine... and save weight!