drop the headliner, unbolt rails from inside the car. look berry carefully at how the trim pieces go together before tearing into headliner, dissasembly and reassembly of the trim pieces is very sequential. good idea to take detailed pix of A B and C pillar trim before pullin stuff apart. athere are tons of weird fiddly fasteners that are easy to break if you rush things.
you do realize there will be 4 gaps in the black trim strips once you remove the racks eh? some ppl just lay black gorilla tape over the gaps, others want a bit more finished look. you can order replacement trim strips from Canadian market subies where they had Impreza wags sans roof racks.
also realize that this is a fairly involved job, not something that you will get done in a half hour after work on a weeknite. allow half a day minimum, plus more time out of the weather to allow caulking in the bolt holes to dry.
I owned a bugeye Rex wag that had the racks removed already. I liked the sleek look but missed the utility of the racks.