Make sure the firearm is completely unloaded before performing this procedure.
First remove the barrel from the receiver. Behind the front sight is a oval slot, cut in the center of the rib, inside this slot is a small round hole. Insert a punch or other suitable tool that fits in the small hole and apply pressure rearward to slide the lock back. This will unlock the rib and allow you to pull the rib straight up and off the barrel.
To reassemble the rib, place it on the barrel stands making sure the rib is flat and the stands are fully engaged at each position. Using your tool push the lock forward until it stops. Reinstall the barrel to the receiver.