My son gave me his iPhone 7 +, but there's a problem.

My son reset the phone to its factory settings before he gave it to me. I got a new phone number and am now using the phone. However, when I message or call anyone who he once messaged or called, it shows his name, not mine. What do I, or the others, need to do to make sure my name only shows up when I message or call them? Thank you in advance for any help.