First, why do you need to get to the plugs? If you're just curious as to where they are, it's probably not worth the effort to get to them.
This is the Yamaha photo of where the plugs are.
In real life, this is where they are.
You need to remove the seat and the gas tank to get to them enough to remove them. I'm not sure on the exact procedure for doing that though. Your dealer should be able to help, or the factory service manual is available now. That would tell you how.