how can i delete the old account and change it to my account
It is my daughters old iPhone 6 but it still uses her old Apple ID I want to delete it and I don’t know her password thank you
If you don't know her Apple ID passcode, you'll need to contact Apple with proof of original purchase and see if they can help you. Can you ask your daughter for the passcode? Or, if she doesn't want to give it to you, have her remove the phone from her account through icloud.com.
What to do before you sell or give away your iPhone, iPad, or iPod touch - Apple Support