I need to give my old iphone to my son. how do i put it in his name?

See this support guide:--> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

If you perform the steps provided in the above article, your model 6 should be as it it were new (your son can use a different Apple ID and a new name)

Just to change the name = Settings>General>About>Name...tap there and input the new name.

Regards

Giulio

What I would do is completely erase the phone and then set it up as new using his Apple ID. See: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

and

Set up your iPhone, iPad, or iPod touch - Apple Support

You can enter a name for the phone at Settings > General > About > Phone.

Oops Fox... didn't see your reply in time, sorry.

Giulio