I lent my iPhone to someone who logged into iCloud with their apple ID. Now I want to change the iCloud account to my own, which can only be done by deleting the currently logged-in iCloud account. To do that, I have to enter the password for that account, to turn off the Find My iPhone app. There seems to be no way to remove the old account without knowing the password for it.
This is on an iPhone 5, with iOS 7.1.1.