a) Once the centre bolt is undone the agitator should just pull up and out. Unless someone has glued it to the shaft. I have struck that at least twice before now.
b) The drive shaft is part of the gearbox below. The spin bowl is clamped to the shaft. Once you get the agitator off you will see the clamp. Remove the clamp and spin bowl will lift out. What are you trying to repair? If you are planning on replacing the bearings good luck. It is a major job removing gearbox etc. I think from memory you need access to a press to get the bearings off. Long time since I did one of these.

Lincoln Appliance NZ
December 2016