Hi John..The sleeve nut in the center holds the clutch sleeve to the mainshaft..and the rest of the clutch is mounted to the sleeve. So, you can remove it as a complete assembly without undoing the clutch spring nut once the sleeve nut is removed.
You will need the clutch sleeve extractor which screws into the middle of the sleeve.
When using this tool, after screwing it fully into the sleeve, tighten the centre bolt until some pressure is applied and then give the head of the bolt a sharp blow with a hammer. This 'shocks' the sleeve and helps to break the taper fit to the mainshaft.
If it doesn't come right off, tighten the bolt again and repeat...it will come away at some point.
Don't screw in the extractor and then try just to 'wind' the sleeve off...you will probably strip the extractor thread...Ian