its pretty straightforward even for me
you'll need the twistgrip and a new cable made up, typically this means sending your old twistgrip and cable to venhill if thats what you go for. if you do, get them to make the cable about 3cm longer as the oem cable comes under the grip and the venhill is over the top, otherwise you'll have to route the new cable inside the handlebars rather than up and over the front.
the oem twistgrip comes off with a couple of bolts and slides off the end of the bar, the cable detaches from the throttle body accessed vai the lhs side panel, i tied a bit of string round the cable before i pulled it through so i could pull the new cable back on the correct route.
the new twistgrip unit just slides on the bar BUT depending on your handlebars you may have to remove the locking pins that fix the starter/kill switch unit in place as the new twist grip wont butt up against the switch unit. its a bit of faffing to get everything as far on the bars as possible and then trim the tube of the twist grip to fit your barend/handguard combination. I'm using renthal twinwall bars so the amount of space for the brake lever perch and the switch unit is limited due to the step in the bars. i trimmed about 15mm off the end of the tube and then spaced out my handguards to give me enough room for my hand to fit comfortably. i may look for a lower profile switch unit so i can do away with the spacer in the future.
the cable attachment to the twistgrip is via the front face plate so thats nice and easy. if you want to change from the fast to medium settings you need to remove the twistgrip unit from the bar, undo a couple of screws , turn tube around and then refit.
hth
