Remove the ottoman lid and set it aside.
Position one hinge inside the storage ottoman 1 or 2 inches from a corner along the top edge of the ottoman, where it will connect to the lid.
Screw the hinge into place using the longest screws possible. The screws must be shorter than the thickness of the ottoman so they don't poke through to the outside. Install the second hinge on the other edge of the same side of the ottoman.
Lay the ottoman on the same side on which you installed the hinges. Lay the lid flat on the floor at the point where it will connect to the ottoman. The lid and ottoman should be touching as if they were already connected.
Extend the hinges to rest on the lid, and mark the holes with a pencil. Create starter holes in the ottoman lid using a drill bit that is smaller than the screws, or start the screws in place.
Attach the lid to the hinges with screws that are slightly shorter than the thickness of the lid.