Will second or third the warning not to use petroleum products to remove or install grips... this will cause them to slip at the most inopportune moment.

Preferred method is to use a compressor but know that not everyone has access to one.

An old trick I used to use was to put a little soapy water into an insulin syringe (with a needle) which can be inserted into the middle of a rubber grip, this does not damage the grip and you would be hard pressed to find a mark.

A tiny amount of soap injected into the middle of the grip will make it come off very easily when getting soap in through the ends was sometimes difficult.