To swap a flywheel the steps are as follows-
Drain engine oil
Remove Sprocket cover and case saver
Once that is done you should be looking at this (i had my chain removed for cleaning, you should be able to move it out of the way since the back wheel will be coming off but more on that later) -
Next you will need to remove the three 8mm bolts from the starter gear cover which sits above the alternator cover.
There will be two additional bolts inside of here that will need to be removed in addition to the 8mm bolts around the periphery of the alternator cover. The starter gear will need to be removed, it should just slide out.
Once that is done you should be able to pry the alternator cover off with some wiggling. There is an o-ring on the starter that can make this a bit tricky as well as possible gasket stickiness.
When the cover is off you should be looking at this but note that there will be an additional gear set that will interface with the flywheel gear (mine is removed in this pic, it sits in the bushing hole at the top right of the flywheel). I have heard you can remove this gear with the flywheel still installed but I was unable to, not a big deal. Be sure to check this bushing for damage as they have been known to wear out prematurely (not common however).
Now we will need a way to keep the engine from rotating while we remove the bolt holding the flywheel on. I used a chain clamp.
Once the bolt is free we need a method of pressing the flywheel off the crank. You can use a fancy tool for this but I used the rear axle since it's the right size and thread. You may need to re-position your flywheel holding apparatus to keep the engine from turning.
Once you have the old flywheel off make sure your starter ring and shim are in proper orientation as well as the key for the crank and you can install your lightened flywheel. Getting it back on can take a few tries but since it is keyed it's impossible to put on the wrong way (unless you forget to use the key). Don't forget to put your starter gear back into its bushing like I did the first time, luckily I didn't have the bolt torqued back down.
Tighten the flywheel retaining bolt to 88.5 ft lbs.
I was able to reuse my original gaskets and have not detected any oil leaks, but it wouldn't be a bad idea to have new gaskets on hand in case they tear while taking things apart. Reinstall everything in the reverse order and refill the crankcase with fresh oil and enjoy your new, quicker revving KLX !!!