Chapter 9 - Deleting Backups

Phones, both iOS and Android, regularly back up all their data to either Apple or Google. This is done so that if your phone is damaged or lost, you could recover your contacts, messages, photos, etc.

A problem arises when we wish to remove information from our phone. Even if we remove an app from our phone AND factory reset the phone, an old backup still would have the data from that app in it.

A good way to deal with this is to delete backups after removing any apps or data you want off your phone.

Deleting Google Android backups - 
From your phone, go to Settings -> Google -> Backup. Turn off "Backup". Select "Turn off and delete". Re-enable backups if you want to resume backing up your phone. 

Deleting Apple iPhone backups -Go to Settings > [your name], then tap iCloud.Tap Manage Storage > Backups. Tap the name of the device whose backup you'd like to delete. Tap Delete Backup > Turn Off & Delete.When you delete a backup, it also turns off iCloud Backup for your iPhone, iPad, or iPod touch. You can turn iCloud Backup back on in iCloud settings on your device. 
(from https://support.apple.com/en-us/HT204247)