Turn the chair upside-down so the rails are pointing upward. Have an assistant help you if the chair is too heavy to manage on your own.
Remove the bolts holding the rail assembly to the base of the chair. There are usually four or more of these bolts, but the precise number depends on your particular model.
Slip spring spreaders between the springs on each side of the chair to prevent them from closing when you move the rails. Stiff springs like these are extremely difficult to open if they close completely.
Remove the remaining screws holding the springs to the rocker assembly. The spring spreader now prevents the springs from snapping shut. Lift off the rails and place to one side.