How do you turn up a speed governor on a 2011 freightliner cascadia?
Take it to a shop which has the appropriate software (DDEC for Detroit or Insite for Cummins), and they can change the parameters. If it's your truck to do this with, you should already know the ECM password.
By speed limiter do you actually mean "governor"? This device to the best of my knowledge was designed to disallow cars from reaching 110mph and/or 124mph on certain models. You should call Chevrolet to confirm this - I doubt if they'll tell you how to lower the top speed it allows because if you have that knowledge then you will then know how to increase the top speed.
It has a stock governor at 135 mph witch can be removed but not replaced or changed now on the 2011 mustangs there is an option called MYKEY witch allows a parent to have one key that has no restrictions and one key (for your child) that limits speed to 80mph stereo sound to 40% and the seatbelt chime will not shut off until it is buckled. Hope I answered your question hahaha