You've got to remove 2 tight bolts that hold the calipers on. You'll need a long breaking bar for this. I'm going to put some penetrant where the rotor contacts the wheel assembly near the center. I'm then going to wack it off just like I did for the rear drums.

When it's off, clean off as much rust as possible on the wheel assembly and put on some high temp anti-sieze compound before putting the new rotor on.

Before attempting to drill out the screws, try this link:
http://www.motorcycle.com/mo/mcnuts/stuckscrews.html.