Raise the tank. I can't remeber if the airbox has to come off to gain enough clearance.
Split the control housing (two phillip head screw) You should be able to loosen the control cable with the various adjustments to get enough slack to take the cable off the throttle grip barrel. Then it is pretty much plug and play swapping them. Watch for the pin in the housing when you start putting the housing back together. It locates the housing to the bar. Then adjust the slack.