Because human height cannot be adjusted, it is left to the bench to adapt to the height of the organist. For organs played by only one organist, modifying a bench to meet his or her needs alone may be enough. For organs played by organists of various heights, the bench must be made adjustable in some way. Adjustable benches can be raised or lowered by a crank or other mechanism. Such benches require an investment (often over $1000-$3000 each), but may serve the needs of organists of any height for many years.
Once you bring the bench to the optimum height, measure with your fingers the distance between the bottom surface of the top board and the top edge of the bench legs (see video example). Return the bench to this height each time you play.