pin at the back of it, near the selector switch. push that out, there is another at the front that can be removed, depending on what you want to do. if you want a barrel change, jsut pivot the gun on it, it should swing around quite easily. if you want it removing, just remove the front pin too and disconect the battery wires from the reciever wires (little plug near the barrel/reciever/foregrip joint)