there are two metal clips behind the headlight unit, they are long and attach to the top and bottom, and clip into two grooves. With a bit of working they should come out of their little grooves. They don't come off entirely but they come out.
The back of the unit should come off easily.
However, if it's the left side you are wanting to change, then you may have to remove the top of the air filter box, and move the air intake around a little to get to where you want to be.
Hope this helps,
Jay
HNC-JAY
January 2009