Rotate the couch with an assistant so the top surface is facing the ground and the legs are pointing into the air. Expose the legs by pulling back any fabric that is fastened around the edges of the legs.
Remove the legs by taking out any screws with a drill, or by twisting the legs counterclockwise in the case of legs without visible attachments.
Position the new couch wheels in the four corners of the couch, in roughly the same places in which the legs were attached. Mark the screw holes -- which are a part of the wheel bracket -- on the couch wood with a pencil. Position the remaining two wheels in the center front and the center back of the couch, and mark the screw holes in a similar way.
Pre-drill all of the markings with 2-inch holes using a drill bit with a diameter not as large as the wood screws.
Attach each wheel by screwing in each wood screw partway, then tightening them all once they have all been installed. Repeat this process for each of the six wheels.
Flip the couch upright slowly and make sure the wheels are fully bearing the couch weight and are swiveling and rotating properly. Once it is in position, lock the wheels of the couch by flipping the locking mechanism, which is a part of the wheel assembly.