A factory service manual is a wonderful thing... on the right hand make sure you wedge a small piece of cardboard in the brake lever. There is a small switch in there that controls the rear brake light... it is fragile and many a person have broken it.
You need to adjust the throttle and idle cable to give enough slack to release the barrel ends from the old grip. Roll back the protective rubber cover to get to the nut. Be careful as those barrels on the end of the wire have a tendency to go flying or fall on the floor never to be seen again.
To remove the left grip you might have to cut it off. I did when I did mine.