just slice the old ones off , clean the bar and throttle then
1) Cut a disc of foam the same size as the flange end of grip and cut a hole in the middle of the foam disc slightly smaller than the hole in your grip where it slides on to the throttle
2) slide the foam disc on - this will act as a throttle filter preventing dirt getting into the throttle body and creating throttle stick.
3) get your new grips , get some adhesive I recomend 5 minute araldite over hairspray as hairspray is piss week. spread a little bit of glue on the throttle tube but away from the edges then slide the grip on and squeeze the grip
4) let it set for 5 mins then locwire with 0.5mm stainless steel or copper wire ( as their soft) and wrap around the grip twice and repeat process 3 times on the grip. wire against the flange , wire in the middle and wire about 10mm from the end of the grip. Twist wire ends with vice grips and leave a 2 mm gap when streched and cut excess wire. Press the remainig twisted strand into the grip
5) Repeat process for other side of bar
*Also a good idea to wack some dowl in the end of the bars to prevent bar damage if you dont run bar ends