Exactly what Jesstzn said. I used adhesive remover (3M brand) when I removed my rear emblems. It wasn't impressing me, and was needing a lot of rubbing. So I soaked a rag in WD-40, then layed it over the remaining adhesive for a couple minutes. Remaining adhesive just wiped off. I thought this was safer than trying to rub a lot with the adhesive remover. When removed, wash area, polish to blend any fading/marring, and wax. If putting on a new one (hopefully with screw on clamps), treat the rubber weather seal first, and get as much wax under it before mounting as you can. I also waxed my entire deflector to make cleaning much easier (they're tricky to really clean under when mounted, as you probably know).
On my '97 Maxima, I've noticed my factory deflector actually increases wind noise when the sunroof is closed. When I have my sunroof open (either vented or slid back), I want the wind and noise coming in, which the deflector somewhat prevents. Anyways, mine is off for now, and the car looks "sleeker" IMHO. You may like yours off, too. Try it for a few days to see what you like.
Hope this helps.
Dave