You can't do any of those while the vehicle is in motion.
Okay, we change up and down through the gears.Note my corrections above. No, we don't say that. In BrE, we "change gear", not "shift gear".
In 1 and 2, using "change up" and "change down" would be understood to mean that you're talking about gears. Do you drive a car?Okay, we change up and down through the gears.
Do we say the following?
1) I changed
the gearup to increase the speed.
2) I changed
the geardown to stopslow the car/motorcycle.
3) I put the motorcycle in
5thfifth gear to increase the speed.