The shifter inner cable can be disconnected easily by rotating the shifter pulley backwards so that the cable goes slack. Shift to 8th gear before. Once the cable is unhooked from the pulley, the cable outer is disconnected by moving the cable housing spigot out of the fulcrum lever. The axle nuts can then be loosened to remove the wheel. It is a very simple procedure.

Note: The shifter pulley has a hole somewhere on the back, you can stick a 2mm allen key in that hole to aid in rotating it backwards.

Note: The spigot has flats so it can't be just moved out of the fulcrum notch - it has to be rotated slightly so that the flats aligh with the notch flats. None of this is visible if assembled, so experiment. Just don't force it.

Basically the reverse procedure of the first pic. The second one shows how to adjust it, probably not needed.