Swap any two wires from the ESC to the motor. It'll change direction, no problem. The motor looks the same to the ESC regardless of what direction it's going. Don't even think about reversing the battery leads -- that would be bad, in a smoky, maybe fiery, expensive sort of way.
If you want to just try it out, reverse the motor direction, put on a clockwise prop, and leave the spinner off.
Note that the effect that reverse-rotation props have on flight is moderately subtle, and change the required trim of the airplane. If you reverse rotation and the plane immediately flies better, it doesn't mean that reverse-rotation is better -- it means that your plane was poorly trimmed, in a way that just happened to be more right for the backwards prop!
Note, too, that the top guys all went over to reverse-rotation about six years ago, and all the 2nd-tier guys followed. Then the top guys found reasons that the good old counter-clockwise direction was better, and they've mostly gone back.