You can change out your brush head by lightly gripping the handle in one hand, head in the other with the bristles pointing away from you. Gently pull the head off the handle in a slight arc motion as shown in the video below. Do not snap the head directly backwards.
Hold handle in one hand, head in the other, bristles pointing away from you. Gently pull head away from handle while also applying light pressure backward towards you, as shown in video above. Dampen old head bristles and use to remove paste from handle. Pull motor out using “ears” then tip handle to tap out battery. Drop in your fresh or charged AAA battery, negative end first then slide motor back in (it’ll spring up slightly) and push new head on until it makes a dull click.