Moving the jet needle clip is quite simple as long as you don't lose the little c-clip when doing it, i made a vid awile back for another fellow, see below. Normally for every 7 deg C you need to change 1 jet size, if it gets colder you need to go to a bigger main jet, if it gets warmer then you can goto a smaller main jet, the one thing you need to know first is if your running the right sized main jet in there already, checking the spark plug will aid you in determining that, plug too black is too rich, a white plug is too lean.
If your unsure about tuning the mikuni carb i would read through this
http://www.iwt.com.au/mikunicarb.htm it will explain what jet handles which part of the throttle position and how to adjust them, the main and pilot jet are simply changed by removing the fuel bowl from the bottom of the carb and then unscrew the old and in with the new.
And one other pic for reference
