Danger! Your autofocus may never work again if you proceed past this point.

Remove the four screws from the inner base of the zoom ring housing. They will require some torque to get them out. Make sure your screwdriver has enough 'bite' and push down while turning. Get your friend back in to hold the barrel steady.

The housing will try to spring up; unscrew the screws evenly and apply some downward pressure on the housing as you remove the screws.