Changing the transmission fluid is a maintenance item you do at 1000 miles and then every 5000 miles after that. These instructions work on a 2005 XL1000C but you it's a good idea to get a manual for your bike if you intend to do your own maintenance.
2. Put the bike on the side stand, place a pan under the bike and remove the transmission drain plug.
3. Take off the primary chain inspection cover. Check the o-ring on each of the two hex socket screws and replace as necessary.
4. While you're waiting for the fluid to drain check the primary chain free play. It should be 1/4 to 3/8 inches with the engine hot (see note 1 below).
5. Put the bike on a jack so it's level - this allows another few tablespoons of fluid to drain out of the primary. (see note 2 below)
6. Clean the metal shavings off the drain plug.
7. Inspect and replace as necessary the rubber o-ring on the drain plug.
8. Install the drain plug and torque it to 14-21 ft-lbs.
9. Add 1 quart of HD Transmission fluid into the primary chain inspection opening.
10. Install the primary chain inspection cover by putting a little blue Loctite on the two hex socket screws, and torque them to 40-60 inch-lbs.
The official way of changing the transmission fluid involves removing the derby cover and adding a quart of fluid or adding fluid until it reaches the bottom of the clutch diaphragm spring. I figure if the HD owner's manual calls for a quart I can drain the primary and put a quart in without anything blowing up. There may be other oils you can use in the primary but picking up a quart of the HD transmission fluid gives me an excuse to go to a Harley dealer every so often.
Note 1 - Primary chain adjustment is at the same interval as engine oil and primary fluid change - at the first 1000 miles and then every 5000 miles. I adjusted my primary chain at 1000 miles because it was loose. Checked it again at 5000 miles and it was still in spec. I'm assuming the chain stretched when new, or the adjusting shoe wore some, and have started to stabilize now that they have some use.
You adjust the primary chain by loosening the adjustment locknut and turning the adjustment screw inside that locknut. Clockwise tightens the chain. After you have the slack correct (3/8 to 1/2 inch for a cold engine or 1/4 to 3/8 inch for a hot engine) tighten the locknut to 20-25 foot-lbs.
I've put pictures of the primary chain inspection cover, the primary chain adjustment locknut and a quart of HD transmission fluid below.
Note 2 - Regarding need for a jack. You don't really need a jack to do this task or to change the engine oil. Just hold the bike upright for a minute or so to let the last bit of fluid drain out. I use the $20 Bike Lift which works fine and doesn't take up much room hanging from the rafters in the garage.
One final note - regarding torque values. I like to use a torque wrench for some things where stripping a thread or having a nut/bolt/screw fall off could be dangerous or expensive - but I'll resort to good and tight, pretty tight, or snug but not too tight - for a lot of things. Of course it's up to you to decide what works best for your particular circumstances.