Lay the paneled room divider out on a flat surface, such as the floor or large table. Place it in the open position.
Unscrew the hinges that connect the inner panel to the outer panel. Leave them attached to the outer panel. Set the outer panel aside.
Flip the remaining two panels over so you can access the hinges on the other side. Unscrew them and remove the inner panel.
Line up your replacement inner panel with the hinges on one of the outer panels. Use a drill to make a starter hole for each screw if necessary. Screw the hinges into place on the new inner panel.
Flip the two panels over and line the other outer panel up with the inner panel. Drill the pilot holes and screw the hinges in to complete the replacement process.