How do I log out of extra Apple IDs on my macbook air?

So someone gave me this laptop, and I love it, but sometimes I will get a call from some stranger who is trying to call that person. I think that their apple ID is still inside my laptop somewhere, and I need to get rid of it. Today I even got a pop up saying something like, "Your apple ID has been logged into on 'person's name's' phone. If this is you, press ok." But ok was the only option to press. Please help me!