If you still have access to your old email address, go to https//appleid.apple.com, click Manage my Apple ID and sign in with your iCloud ID. Tap edit next to the pimary email account, tap Edit, change it back to your old email account and verify it. Then edit the name of the account to change it back to your old email address. You should then be able to turn off Find My iPhone with your password. Then go to Settings>iCloud, tap Delete Account and choose Delete from My iDevice when prompted (your iCloud data will still be in iCloud). Next, go back and change your primary email address and iCloud ID back to the way it was. You will then be able to go to Settings>iCloud and sign in with your current ID and password to reconnect to your iCloud account.
If you don't have access to your old email address, you will have to contact Apple to get them to reset the password for it so you can disable Find My iPhone and sign into your iCloud account. You will have to prove your identity to them in order to do so. You can either contact iTunes support for assistance with this (https://ssl.apple.com/emea/support/itunes/contact.html), or contact Apple Support (http://www.apple.com/support/icloud/contact/).