In the old rules you would loose your "ranger" abilities and become a "Fallen Ranger" if you did something construed as "evil". Not sure if 5e enforces that, but as Rangers always used to be good aligned, and they got powers from deities.... committing evil acts would cause those loss in abilities.
5e has basically done away with all alignment-related restrictions. I suppose Paladins can still technically become "Fallen," but that's due to breaking their oath as opposed to acting as a different alignment. Rangers have absolutely nothing restricting them; I don't think they even necessarily get their spells from a diety, and I certainly haven't seen anything about them losing their powers.
