Aussie easiest way if you have an air compressor is to remove bar ends weights then blow off old grips by wedging air nozzle under outside lip of grip. When you hit it with air, it will expand and pull right off..almost fly off as a matter of fact. Then start the new grip on, stick the air chuck in , kind of close the end of the grip around it and blow the new ones on. OR spray some hair spray or contact cleaner in the new grips, sling out amy excess and slide those puppies on. Be careful not to get the throttle side tight against the throttle housing which may keep the throttle from returning.
If you don't care to save the old grips and don't have air, you can always use a razor blade and slice them off. Remember there is a plastic throttle tube under the throttle grip.
Then put your bar end weights back on
( I use the air from the other end not like this guy but you get the drift)
http://youtube.com/watch?v=xg3w1YnQBVo
http://youtube.com/watch?v=tL3_3_4pdcY