To disable iCloud from an iOs device, the device's backup must be removed from the cloud. The exact method for doing this depends on whether it is being done via iOs directly or with a Macintosh or Windows computer.
The process of removing the iOs device from the cloud directly depends on the iOs version. For iOs 7, go to Settings, click on iCloud and then select Storage & Backup. Next, tap Manage Storage. For iOs 8, go to Settings, iCloud and then Storage. Next, tap Manage Storage. For both iOs versions, the final step is to choose the name of the device you wish to remove and then tap Delete Backup. This removes existing files on that device from the iCloud backup and also prevents the device from using the cloud.
The backup device can be removed from the Mac computer by clicking on the Apple Menu, selecting System Preferences and then clicking on iCloud and then Manage. Select the device on the left, and then click delete.
Backup devices can also be removed via PCs by opening the iCloud for Windows program. For Macs, click on the unwanted backup device on the left, and then click delete. For both the Mac and PC, if no devices are visible, then the iOs devices do not have iCloud backups.