How do I perform an arms overhead ball crunch with rotation?

Lie on a stability ball with the ball placed under your low back, bend your hips slightly and keep your knees lined up directly over your ankles. Your feet should be placed flat on the floor, hip width apart. Extend your back over the curve of the ball and extend your arms overhead. Draw-in your navel and contract your glutes. Crunch your upper body forward and rotate your upper body to one side and then return to center. Lower your torso back down to the starting position and repeat, rotating to the opposite side.