bought iphone 4s second hand, and im having trouble activating it.

so i bought an iPhone 4s second hand, and I'm having trouble activating the phone, its linked to the persons apple id and

its asking for the person to sign in and i no longer have contact with him.

I went to a Verizon store, and they said that i myself can do it at home by connecting the phone to iTunes, but i don't

know what or how to do that, please help.