how can i delete an icloud account that was left on my iphone
so basically my sisters bf gave me his old iPhone 4, but left his old iCloud account logged in with find my iPhone on and i can't delete his old account because he forgot the password, I've signed into everything else with my account but keep getting pop ups asking for his account password, all i want to do is factory reset the phone and then back up one of my old iPhone back ups which has photos i want on my iPhone. please help me if you can
iPhone 4, iOS 7.1.2