Handgrips are meant to be tight and not slip. To loosen just put a flat head screwdriver between the handlebar and the handgrip and slowly push between handlebar and handgrip up to 1 1/2 inches. Pry up to separate gently and squirt Windex in the space created. Do this in three or more locations than twist left and right to break the seal. The handgrip should slide right off. To replace with a new handgrip lubricate the handlebar surface with Windex (or hairspray if you need to tighten them up) than while twisting left and right slide the new handgrip onto the handlebar quickly. If replacing the old handgrip than just make sure it is dry and than follow the instructions for the new handgrip. Get it on all the way than let it dry (10 minutes or so) and the handgrip will firm up. If the handgrip is stubborn and fits tight you can soak the handgrips in hot water to soften the rubber than use Windex to lubricate and follow the same instructions. We have replaced handgrips that go on almost all the way and become very difficult. The last inch and a half could be pounded on with a rubber mallet or rawhide mallet. Do not use a steel hammer as any metal to metal like the back end of the handlebar and a hammer that can cut right through the rubber. If the original handgrips are just loose you might try the hairspray to tighten them up.