Like all pitching machines, a changeup is attained by lowering the speed of the wheels. The resultant drop in speed causes gravity to have more of an effect, however, causing the ball to drop faster. Consequently, when you reduce the speed, you also need to manually make an adjustment to the pitching machine head, raising it so that the pitch does not drop out of the strike zone.
There is only one pitching machine currently on the market that is capable of switching pitch speeds and even pitch types and automatically adjusting itself so that it always is throwing to the same location in the strike zone. It is called a Spinball iPitch and currently it costs $10,000. They will be raising the price in January 2021.