Hello Katie and thank you for your question.
First, turn the fixture off and allow bulb to cool before handling. Remove the lens/diffuser by lightly pulling the front edge while pulling downwards; it should pop out easily. Remove the bulb by grasping the ends of the bulb and rotating until the bulb becomes loose. Pull it straight out from the lamp holder while being careful not to drop the bulb. Grasp the replacement bulb in the same manner and reinsert into the lamp socket. Turn tube until it is securely held in place. Do not use excessive force when installing the new bulb. Finally reinsert the lens/diffuser.
Refer to the diagram shown in the “ Bulb Replacement Instructions” section of the Instructions located here: http://www.homedepot.com/catalog/pd...
Best wishes on your project.