The middle button marked UP/OUT tilts the motor up as far as the trim limit. This limit is the upper most point that the leg is supported in the transom yoke. The motor should not be operated above idle with the leg any higher than this point.
The upper button marked UP tilts the motor all the way up.
This is what I remember from digging deep into a dim distant past so even though I'm reasonably certain that is how it worked I wouldn't bet my lefty on it.