[Sid Squid]

You'll need a stand of some kind or at least some way to prop the bike up with the rear wheel off the floor.
Before lifting the bike up, loosen off the rear wheel spindle nut, and although not strictly necessary it's easier if you remove the rear caliper, undo the two bolts - and the torque arm bolt on a curvy - and hang it out of the way.
Lift the bike up and remove the spindle nut, supporting the wheel remove the spindle, it should just pull out but it's not unknown for it to be a bit stiff, if you should need to drift it out with a rod of some sort, take care not to damage the thread, disengage the chain from the sprocket and remove the wheel, grasp the sprocket and pull it away from the wheel, it can be tight in the drive rubbers, but if they're loose in the hub when the sprocket carrier is out, remove them and put them to one side whilst the wheel is off, don't lay the wheel down on the disc it can be damaged, ensure you have recovered all the spacers, a flanged one on the right, a plain one on the left, and there is a spacer you won't need to remove but often falls out anyway in the sprocket carrier.