Stop. Before you do this, you may want to mark the centre wheel in some way.
Removing the pins: A gentle prise from under the coupling rod with a fine screwdriver will release the pins. These are metal on this loco. The centre pin holds the con rod which is linked to the valve gear. Probably better to remove the valve gear before the wheels rather than have it flapping around with the chassis not elevated enough to clear the delicate mechanism.