Very, very easy! In trunk, you'll see a few little holes to pull back the felt type covering over the rear of the light assembly. Upon doing so, a plastic cover is revealed with a turn knob that unlatches the plate to which the light bulbs are mounted. Simply replace the burnt out bulbs, (push down/then turn out) with the same type bulbs. The bulb model # is on the plate next to the socket for each, or is embossed on the bulb itself. These bulbs are available almost everywhere - even grocery stores - very inexpensive. Trick: MB has been thoughtful enough to provide a few spare bulbs you'll see mounted right on the plate itself. Replace and lock plate, push back felt. Done deal. Maybe 2 minutes (after you've done it once). Another trick I've learned: Always look closely from the exterior to identify which bulbs are burnt, but especially the ones behind the red lense (running litghts), there are actually 2 bulbs...when 1 is burnt out it is still hard to notice that from just looking. Also, it's rather common that when one blows, the other side is nearing the end of it's life too.