My house is on three floors, it has central air conditioning, the
thermostat is on the middle level, and there's an exhaust fan on its own
thermostat in the attic. When the temperature is comfortable on the
middle floor, it's too warm on the top level. It's a bit cooler on the
ground floor.

What's the most effective, assuming any of them is effective, of the
following approaches?

1. Partly close the incoming air vents on the middle floor and possibly
the ground floor. The theory: a relatively larger portion of cooled air
will go to the top floor.

2. Hang a ceiling fan in the stairway between the second and third
floors to push the air upwards.

3. Hang a ceiling fan in the stairway between the second and third
floors to push the air downwards.