easy
put seats about half way down enough to get your hand/arms round it
undo the screw that holds the plastic cover on and slide it out
reach round the seat and either
feel which bulb holder to remove, thats the difficult bit working out which one unsighted
or as already said
undo the retaining plastic nuts and slide the whole unit out
there are 2 retaining plates, held in with long plastic threaded nut affairs, bolt come from light unit with a u shaped strip of metal that holds light unit by pressing against the body work
undo those, take them out and light unit will come out be careful not to damage the foam gasket thing our water will get into car
WD 40 the light unit, electrics and threads before putting it back in in reverse order.
Only thing to be careful of is not to drop the second plastic nut or bar into bottom of the body work, as you will have to take first off to get it out through light unit hole
Fiddly but not impossible