Adjust the head support by pressing the sides of the buckle inwards. This allows you to pull it up or down, like a zip, into the desired position. You then tighten the strap as much as required.
To fold down the head support, start by gripping the buckle for head support adjustment and pulling it down as far as possible (you may need to loosen the strap if it is too tight). Fold the head support outwards. Tighten the strap to keep the head support folded down.