easy as falling down but you might need new trim clips.
unscrew the two bits of plastic trim either side of windscreen. remove.
remove rear view mirror arm - unclips - then unscrew mirror base.
unscrew the sun-visors.
then carefully pry off the white plastic clips, knackering a few in the process, carefully lower the roof lining and reach up between it and the roof and disconnect the light wire and unscrew the earth fixing. (some light designs are different and you may have to remove the light before lowering trim)
job done.
(can be difficult getting the roof trim out without folding it)