This is by far the easiest way to do it and takes 5mins.
1)Take sidelight out 2/3 screws depends on little or big sidelights,this allows you to pull the grill out a bit if needed.
2)4 screws that hold the black plastic surround on around the light unit,give it a wiggle about to get it off as it wedges under lid at top(it can catch on grill or sidelight as well)See no1
3)4 bolt screws that hold the top lid on.
You can now get to the bulb holder at the back of light