We just finished changing out our rear center brake light for a Kia Optima 2006.5. Took my husband and had to have my help too because you definitely need 4 hands!
Remove the small screw holding the light assembly -- look inside the trunk and find the circle hole with the electrical cord/clip that is directly below the brake light. Then unclip the wires holding the light wiring assembly. My husband removed the clips as stated above (not sure how he did it).
From inside the car, push down on the rear window panel while pulling up and out on the rear break light assembly. There's a metal clip in the front -- push down on the rear window panel and up on the light assembly to get the light past this first. Take care to guide the brake light wires and wire clip around the cut outs that hold the wire in place. There are two bracket-like clips that hold it in place in the rear, nearest the window -- push the light assembly down in the back and tilt up tin the front to get it past those.
Once the light assembly is out, it is easy to swap out the bulb. Repeat all steps to get the light assembly back in place -- guide the back, L-shaped tabs back into the rear window panel and snap the silver clip in place. Go back into the trunk and reattach the light wire clip, replace the screws. Not sure about the other clips. Have 2 adult beverages handy to two celebrate because Kia has designed a really screwed up way to replace this light.
TIP: From inside the trunk, pull open the back seat for a better angle and you can have a second person help if needed.