The switcher in your photo looks very much like an old Rivarossi SW1500/SW1200 model that Kato built a new mechanism for. The original Rivarossi switcher was way too fast for an express passenger locomotive, let alone a switcher. The Kato drive got the minimum sustainable speed down to under 100 scale miles per hour, but it was still awfully fast for switching. If it's what I think it is then a pair of small screwdrivers, inserted between the plastic shell and the metal frame, near the fake flat "fuel tanks", should spread the shell enough to pull the mechanism out. Many. though not all, model locomotives use this same scheme for holding the shell on the mechanism. If I remember correctly, the cab and the hood were separate pieces, so you might be able to pull the cab off first, and then the hood.