You first need to remove the floating part of the calipher (remove the 2 slide pins and remove calipher) and then unfortunately you need to remove the calipher mounting bracket which keeps the disc 'trapped'.

Cleaning the bolt head well and using some sort of impact tool with a 6-point socket (either an air-wrench or a bar and hammer) usually can break it loose.

After that's removed then you can remove the brake disc. Front discs are separate from the bearing, rear discs usually are a single unit with the bearing pressed in. Early models with rear disc brakes also used separate disc/bearing units.

Bye, Arno.