Grips on your bike are pretty important. You need something soft and comfy to hold on to when you come flying off of a hill or some traction when you’re busting some seriously hardcore bike moves.
If you are planning on reusing your grips, however, most of mechanics don’t really have a solution other than cutting them off with a razor or scissors. I did find one tutorial on inflating them off with a bike pump so I’ll include that, just in case. If that doesn’t work, lift off the edge of the grip with a thin screwdriver and drop alcohol in between the stem and the grip. Enough alcohol should get the grip to slide.
Installing them is pretty straightforward. Get a bit of sprayable rubbing alcohol or hairspray and spray the inside of the grip. You want to make sure that that handlebars are clean of residue before you proceed so give it a good cleaning with some solvent or alcohol. Then slide the grips on.
Let the grips sit for a while to allow for the alcohol to dry out. They will slide if it isn’t completely evaporated so take care to let it sit and dry.