Oh it's actually easy...lemme hit you with it.
Get a funnel, a cut-down straw, a drain pan and some 10w30 or ATF dependin on what it calls for.
Put the straw into the funnel and tape it up real good, cause you'll have to fit that into a very narrow fill hole.
On the LEFT side of the trans cover is a level checking screw, it is near the middle and recessed slightly, you can tell it's the right one cause it's the only one with a paper washer (do not lose that washer.)
Unscrew that one.
Now, put the drain pan under the trans and remove the large screw on the bottom, it should be obvious which one it is from it's position, because where it is, it can't be holding the trans together.
(You will know it's the right one, too, cause once you loosen or remove it, oil/ATF is gonna pour all over your hand, no matter how fast your reflexes are, have rags handy.)
Now drain that puppy out.
Now, remove the TOP screw that looks just like it, and without replacing the bottom one, push the modified funnel so it will direct the fluid into the hole...and pour about half a cup of fluid in and wait for that to drain, this flushes the trans bottom and any grit and stuff.
Now, replace the bottom bolt, and fill, slowly, until the fluid just barely starts to seep from the level check screw hole.
Lean the bike so it stops seeping, and quick-wipe the hole with a paper towel, and replace the level checking screw.
Now, lean the bike back and replace the top screw, and wipe down with paper towel or rag, and check screws for tightness and leaks.
It's fairly simple once you've done this a couple of times.
Hope that helps,