snoozer

From that link i assume the off position switch is not allowing to pin to retract into the flash body to facilitate removal. If it was mine i would try to get something very thin between the flash and hot shoe to pop the pin in so you can slide the flash off or try turning the complete camera and flash upside down and give it a shake whilst trying to gently slide the flash off. DO NOT blame me if the above doesn't work or damages any part of the equipment as i said "If it was mine"

Unscrew the locking ring on the underside of the flash gun and slide the flash backwards off the hot shoe, Should be as easy as that.