First, you need to unscrew the 2 gold screws on the black plastic piece in front of them. Then I believe you can pull it and the circuit board out (still connected by a wire). Look on the back of the circuit board where the base of the bulbs are. There should either be a twist knob or a philips screwdriver hole to remove them. Just twist a bit counterclockwise and the bulb will come out. You'll also want to remove the green cover, since it's not part of the bulb, and you'll need to reuse it.
They just twist in and out of the board, once you can get to the back of it.
If you want to change the color of the lights, you can hardwire some small wedge bulbs in behind there also.