After issuing two reminders to former MobileMe customers that they would lose their free iCloud upgrade from 5GB to 25GB, Apple today reduced the storage limits as planned. Customers who have more than 5GB, and who haven’t bought a paid storage plan, will find that iCloud is no longer working.
If you exceed your storage plan on September 30, 2013, iCloud Backup, Documents in the Cloud, and iCloud Mail will temporarily stop working. To continue using these iCloud features without interruption, reduce the amount of iCloud storage you are using or purchase a storage plan by September 30, 2013.
As we’ve previously advised, much of the iCloud storage is usually taken up by iCloud Backups which can be deleted through System Preferences > iCloud > Manage. Those who need more than the free 5GB offered by iCloud can also use Dropbox to store photos and files.