The update is pushing out via the Mac App Store for OS X users, though if you've not seen it yet it's always worth manually checking via Software Update. Windows users should go ahead and manually check for updates...
http://m.imore.com/apple-pushed-out-itunes-update-address-itunes-cloud-issues
http://m.imore.com/apple-pushed-out-itunes-update-address-itunes-cloud-issues