Disassembly Of The Wheels And Gear Boxes

I am taking my Wall-E U command apart... Got the base off and the wheel assemblies out with the gear boxes... how do I get the shaft out of the wheel assembly? The only way I can think of right now is to cut it off. Also there is a wheel supplied with the robot kit I bought... how does that work in assy? I was going to attach the servo with the X piece similar to one of the videos. First I need to detach the gear box from the wheel assy... gonna sleep on it. Thanks!