Cannot delete icloud from iphone because cannot turn off find my iphone.

Hello,

I have an iPhone 4 which was given to me by a friend because it needed to be fixed. I got it fixed and I'm trying to delete the iCloud account that's on it. I cannot delete it because I need a password for the email account associated with iCloud. I do not know it and neither does my friend. What can I do to delete this iCloud account from my phone?

Thanks!

Mark