If you hold the assembly by the shroud (perforated bit), and firmly smack the pointy end (technical term!) of the cone on some carpet it will pop out of the indented line you can see in the above picture.
To refit, flip it around so you bash the shroud down onto the rest of the cyclone unit. The shroud will snap back into the groove. Then push the whole thing into the outer shell, making sure the screw holes line up as it's hard to twist around when all together
If you use a screwdriver, it may crack/mark the shroud.