You get your favourite hammer and tap firmly around the lip of the fan cover. It should then fall off and clatter loudly onto the surface of whatever your working on. Then, find a suitable socket and ratchet, hold the fan with one hand (under a cloth to stop you getting cut) and crack the nut off. Undo it, and, making sure to remember where the washers go, remove the fan and spacer washers. Fan off, you will see a plastic airflow channel bit. 2 screws iirc then that lifts off, then some more screws should be visible, which takes the top of the motor housing off, but it will be held on by the bearing, so youll need to either get a puller or tap gently all around it lots of times until it gives in and slips off. Take the carbon holders off and the armature should pull out/tap the other end with something blunt to pop the other bearing out of the casing.
Should give you enough access!