How to delete icloud without password
Hello! I got an Iphone 5s from someone, and he didn't sign out of Icloud, because he doesnt understand how to sign off and he doesnt even remember te password for the Icloud. So I'm wondering if there is a solution to delete the Icloud from the Iphone, because every 10 second Icloud password request pops up which is quite annoying and would like to get rid of it. So if anyone know a solution please tell me. Thanks in advance
iPhone 5s, iOS 8.4