You can disable iCloud from your iOS 8 device by going to "Settings," selecting iCloud, then "Storage" (or "Storage and Backup" on iOS 7), then tap Manage Storage, tap the name of the device to disable iCloud on, then tap "Delete Backup."
You can also choose to disable iCloud from your device directly on your Mac computer. To do this, open the Apple menu, navigate to "System Preferences," click on iCloud, then click on "Manage." Click "Backups" on the left side of the screen, then select the iOS device you want to disable iCloud on, then click "Delete." If you are not seeing Backups on the left, your iOS device is not currently being backed-up by iCloud.
If you would like to disable iCloud from your device using your Windows computer, you should open iCloud for Windows, then click the "Storage" option. Click "Backups" on the left, and select an iOS device on the right you'd like to disable iCloud from, then click "Delete." As with the Mac computer, if you don't see Backups on the left, your iOS device does not have iCloud enabled.
With iCloud disabled, be aware that your device will no longer preserve your data in the event of loss or damage.