itunes from iphone download to pc

You don't.

If you purchased music from the iTunes Store, you can re-download it from the store on your PC using the same Apple ID you purchased it with originally.

You can not transfer music from the phone to the PC directly.

You need the password for the account you used to purchase/download the music. If you haven't changed the password in 6 years, then it will be the password you had 6 years ago...