As above, with one final tip:
If you want to remove the left handgrip and re-use it, get a long, thin screwdriver and slip it between the grip and the handlebar. Squirt some WD-40 into the gap this creates, and work the screwdriver around the circumference of the handlebar. With a bit of wiggling to work the WD-40 around, the grip will pop right off. Clean thoroughly inside and out with dishwashing detergent and you're ready to re-install the grip on the new bars.