Remove the two rubber plugs from the top cap securing it to the main body of the holder, remove the two screws, look carefully and you will see a small steel spring, on both ends of this spring pack some tin foil/ baking foil (a very small amount rolled in to a ball). Replace the cap top and secure down with the screws. The added material increases the presure the spring applies to the mount preventing it from rotating too easy.
If its rotating on the swivel ball too easily take the top cap off and wind a couple turns of tape around the ball, replace the cap and it should be fine - Mike
Start by removing the two rubber bungs from the hinge which reveals two philips head screws, remove the screws to release the top cap (take care not to lose the steel spring)