If you really want to do it yourself for some strange reason then put them through a door jam. close the door to the point where the door and the jam support the grip. pull really hard till it falls off.
Do this AFTER you soak them in hot water for a few min, and in a door that you don't care about. It will fuck up a nice looking door jam and your parents will be pissed.
^ or just find a vice. i'm sure you could walk into a hardware store and they'd help. just put them in a vise, pull them out, ask to borrow a hacksaw, then be gone.
i did it myself, easy actually, stick a screwdriver otr sumthing underneath grip and pull out o loosen, then pull of, or put some wd40 in there and let it sit for a couple min. get a clamp with razon thing on one side. rotate, cut put grips back on