Your manual should cover this topic with illustrations better than I can with words. Basically, you rotate the machine up on the auger housing -- auger is to the floor. It will balance and stand there. Note: if you have drift cutters, you'll need to remove them. You will definitely want to turn the fuel shut off. Still, some gas from the carb will leak out for a few seconds. I have not worried about that, but I suppose you could run the carb dry if it concerns you. Given that it's the intended service position, I assume the oil is fine -- but I don't know enough to say for sure.
You can then remove the bottom cover (two screws). The reason I suggest doing so before making the adjustment, is that you can watch the teeth engage/disengage and then ensure that they are fully engaged when the trigger is released.
Do NOT put white lithium on the shaft or the teeth. Doing so caused me great trouble last year. You want a grease on the teeth that won't harden up in the cold (I use SuperLube) and some kind of oil (I use synthetic 5W30) on the shaft. That bit of advice came to me courtesy of borat.
