Wait, is it actual popcorn or mud? I see a lot of people call things popcorn (ie the Styrofoam stuff) when its actually mud.

My house was built in the 90s and used mud for a popcorn-like effect. If that's the case, just skim coat it and move on. If you try to remove it, you'll end up damaging a bunch of the drywall and have to skim coat it anyway.