How do you remove the dashboard vents in a Nissan Sentra 86-90?

Most of the times the center vents are part of the radio bessel SO remove the bessel by getting the instructions from "Metraonline.com". If that isn't the case then you may slide a very thin ( flat) utensil in between the vent and the dashboard where it "clips" into. Another one, check the automechanics manuals such as Haynes, Chilton's or Mitchell's. Good luck.