Just to let you know....
I made it at Techshop. They have a work bay where you can work on your car, motorcycle, moped... whatever! There are 3 of them around the SF Bay Area, so it's pretty convenient. There's others around the country and they have lots of tools and workshops. Wood, Metal, Fabrics, Electronics and more. It's rad.
Check it out here: www.techshop.ws
Step 1: Removal of Drive Sprocket
Once the drive chain is off, grab a pair of snap ring pliers. I'm changing from a 16 tooth sprocket, to a 14 tooth sprocket. You will see a snap ring holding on the drive sprocket. Simply expand the snap ring that holds the sprocket to the splined drive shaft, and remove it.
At this point, you can remove the sprocket.
Step 2: Install New Sprocket
After you have the new sprocket on, replace the snap ring onto the drive shaft.
Reinstall the drive chain. You may need to add or remove links from your drive chain in order to properly tension the chain. But that's about it.
Here's the link again on breaking the chain, if you need it...