How to use RotVelocity to control a Motor's speed?

I've gotten a bit confused on how to use RotVelocity and how to speed up or slow down Motors. I can do it with a script, but I just need to know how to control the speed of a Motor using RotVelocity.

RotVelocity is a hidden property of motors, you'd have to either use a script like you said, or you'll have to use the command bar in studio to change it.