Have not tried it yet, but here is the text taken from the N Scale Encyclopedia site on doing so...
"...To remove the long hood, unscrew the two screws that hold it to the chassis (said screws are located on the underside of the chassis, just forward of the front truck). To remove the cab, first disconnect the cab handrails and end-railings (they may be glued, so be careful). Next, rock the cab back and forth (side to side) until it disengages from the chassis...."