You’ll have to access the bulb from the inside of your trunk. There should be screws in the interior of your trunk – unscrew these to access the inside of your taillight. From there, it is simple to just unscrew the old bulb and then screw in the new one. This is pretty standard for almost any modern vehicle (although not all).
You could also ask any employee at the auto store where you purchase the bulb. They are usually more than happy to change it for you free of charge.