I Got this solution from forum contributor saeed.ayman (I want to make sure he or she gets credit for the solution if this works for you)
To delete old backup, follow these steps:
Found this solution after some digging in the internet.
First of all, I couldn't even delete my old iCloud backup.
Follow these steps:
1- Go to Settings-->iCloud-->Storage-->Manage Storage-->Select your device that you are having problems backing up.
2- Wait for the spinning wheel to finish (loading icon beside backup options). THIS IS VERY IMPORTANT (for some reason!).
3- Scroll down and click "Show all apps" (it's stupid, but trust me this is the only way I could do it)
4- Scroll all the way down, and click "Delete Backup" and then confirm deleting. If you got an error message saying that "the backup can't be deleted, try again later" that means you didn't wait enough. Let it finish loading.
5- After Deleting the backup successfully, go back to the main iCloud settings page, and go to Backup. If iCloud Backup is still On, turn it off then On again. If it was off already, just turn it on.
6- Go to the same page in step 1 again, and make sure that photos are off (if you want them off), otherwise just make sure that all the options are ok as you want them.
7- Go back to the Backup page and click "Back up Now".
It took me about 5 hours to get it done, but it now works fine.
Note: If after step 7 you got the same error message that it wasn't completed, just press "Back up Now" again, it should continue and finish. I got it to work from the second trial.
Some other contributor indicated they had to turn find my iPad off before a successful back up occurred.
This was my reply to saeed.ayman,
GGreetings. Thank you for your solution. I had this problem with a failed backup and to add insult to injury lost about 2.5GB of iCloud memory to boot and was unable to retrieve it until I came across your solution. I was under the impression 9.0.2 fixed the 'backup glitch' but it appears it did not. Sounds encouraging that 9.1 will finally fix it? (See posts above) Hope Apple realizes that as of yet it still is a bug in OS 9. I am still not able to make a backup. Backup hangs at about 4 minutes to go with 2.1 GB memory left in my cloud storage. (Manual backup on iPad 3 64 GB iOS 9.0.2, WiFi plus cellular but no SIM card installed.)
I also find that I can not update from 9.0.2 to 9.1 (Unable to install msg during verification stage) I wonder if the 2 problems are related? See threads re 'Unable to install 9.1'
Doug
Victoria BC