Anytime during the game press 'y'. You will stop and so will everyting. ON the top it will say 'slew.' Then Press either F2 to go forward or back and F1 to stop, or press F4 to go up or downward, F3 to stop.
You can also use the Arrow Keys, while in Slew mode, or the joystick. When you are done press 'y' again.