Thanks for coming to us to find your answer. Your tail light assembly can be a little tricky, but it isn't hard with a few tricks.
First thing, you will need to lay down your tailgate and look on the inside of the tail light assembly and you will see two screws there. You will need to remove them with a 10MM socket or a large phillips head screwdriver.
Next, there are two clips that hold the outside of the tail lamp assembly in it's place. You won't be able to see them until the unit is out. Find either a hard plastic pry piece or push a rag into the small opening between the outside rear of your tail lamp and the body and use a screwdriver to gently pry the tail lamp towards the rear of the truck. You will hear a pop that lets you know that the assembly has been removed and that will give you access to your tail lamp bulbs!
Thanks for visiting us and let me know how I can help you further with this or how I could possibly help you in the future!