Hi, It's not an easy task if the bolts are rusted, but you'll find when you remove the hub and brake disc assembley that there are 4 or 5 small nuts and bolts holding the disc to the hub. Mine were covered in muck and not visible until I cleaned it. It may be worthwhile soaking the nuts in releasing oil first as they're quite small and easy to snap. You'll need a block of wood and a hammer to tap the assembly apart after the bolts are removed as it's a tight interference fit.
Hope this helps you.