Replace it from the back, not from the front (there are some metal clips holding on the lens, and it is tempting to try and remove this). Pull off the small square (about 1 inch x 1 inch) plastic block into which the wires are set and that leads into the back of the bulb. Then remove the round rubber cover (this comes off completely). You should now be able to see the back of the bulb. Unscrew the bulb, but before doing so, make sure you check the alignment of the metal spring that holds the bulb in place so you can put it back in (it is not obvious how it would fit unless you check first). You can then pull out the old bulb. Insert the new one without handling the glass of the bulb, and put everything back as you found it.
Simon, August 2007