To change a tripod head, first loosen the tripod's locking mechanism by turning the knob counterclockwise. This should allow you to remove the existing head from the stem of your tripod. Then, take your new head and insert it into the stem until it is firmly in place. Finally, tighten up the locking mechanism once again to secure your new head in place. Once this is done, you will be able to adjust and move around your camera as needed for whatever type of shot or angle that you are trying to achieve with your photography!