How do I update the primary email address used by my Apple ID when using Find My iDevice?
As Tyson says, this might help: http://support.apple.com/kb/ts5223

If you can make your AppleID change back to dan@old.com you should then be able to sign out of it on the iDevices. After signing out the iDevices - change the AppleID again to dan@new.com and you're good to go.

The place to change your AppleID (which is used by iCloud and iTunes and the Mac App Store) information is at https://appleid.apple.com/