how do I change my phones apple ID if someone else had the phone first?

Do you know the previous owner? If you do, have them do what FoxFifth provided. If you don't know them or can't reach them, you cannot change the Apple ID at all. If it is Activation Locked, the phone is useless and you can't use it. Apple won't help you and we can't help you. If this is your situation, get your money back or recycle the phone.

I wrote this user tip about used phones --> The All Too Common SAD Reality of Buying … - Apple Community

Have the previous owner do the following: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support