Various thought on that. But be aware the handlebar heaters are under them anything sharp will ruin them. Some say using a hair drier to heat them up and pull them off. This may vary with model of sled.
Drill out the rivet.
Run the sled, put the warmers on high, let them heat, twist and remove.
I did it this way and was able to reuse the grips on new bars.
Yes, as already mentioned, get them really hot and then twist off. A heat gun makes it easy, but don't melt anything. Be sure to drill the rivets out. Don't twist unless the whole grip is free or you can damage the elements inside them.