Open the storage bench and unscrew the hinges which are currently attached. Remove the hinges and reposition the storage bench lid on top of the bench.
Position the piano hinge on the side board of the storage bench, either on the top surface of the storage bench side board or on the outside surface of the storage bench side board, depending on the thickness of the board and the desired look. Arrange the hinge so its other section falls directly underneath the storage bench lid and the entire hinge is even. Mark the location of the screws holes at least every 12 inches along the side board using a pencil.
Drill out holes at each marking, being careful not to go through the board to the other side. Reposition the hinge and attach the hinge to the side board with 1/2-inch wood screws.
Position the other half of the hinge on the underside of the storage bench lid with the help of an assistant. Mark the location of the hinge's screw holes every 12 inches on the underside of the lid using a pencil. Drill holes in each marking and attach the piano hinge to the lid with 1/2-inch wood screws. Test the lid for swinging operation and smoothness, and make any necessary adjustments by removing screws and installing them in new holes.