Wont let me sync on a different computer without erasing all my music
I am using my dads computer because mine is broken and i logged him out of the itunes and logged me in and there were still a bunch of random songs on the account they werent mine or his, so i go to sync my phone and itune says it cant sync my music without deleting all my music and replacing it with the songs that are on the itunes account already, how do I go about getting all my music onto the computer?
iPhone 5s, iOS 8.1.3