Make sure that your child meets all of the size requirements to use the Pico: at least 1 year old (recommended age 2+), weighing at least 22 pounds, and at least 30" tall. Once you have properly installed the Pico, open and loosen the harness system, and adjust the headrest upward to its "Lowest Use Position" (headrest above seat back). Place your child in the seat, place the harness straps over their arms and shoulders and buckle each buckle tongue into the buckle. Pull all of the slack downward, towards the buckle, and tighten each harness strap at the hips. Ensure that there is NO slack in the harness system (check by assuring you can not pinch the harness webbing vertically), then clip the chest clip together and adjust it at armpit level. Raise or lower the headrest (as needed) so that the tops of the child’s ears are below the top of the headrest, and then check to make sure that the child’s shoulders are below the top of the harness system to assure proper fit. Please don't hesitate to contact us for help.