Use a small iPod opening tool to flip up the black plastic tab holding the orange click wheel ribbon in place. The black tab will rotate up 90 degrees, releasing the ribbon cable.
Use a small iPod opening tool to loosen the click wheel cable from the logic board. Be careful not to bend the cable too much, or the electronics on the cable could be damaged.
Disconnect the click wheel cable from of its connector, and lift the entire click wheel assembly away from the logic board.
The click wheel should now be separate from the rest of the iPod.