Welcome to Android Central! Can you please clarify your question? Do you actually want to keep your Auto Backup photos, or delete them?
Auto Backup is a feature that automatically backs up any photo you take with your phone to an Auto Backup folder in your Google+ account. You can turn the feature on or off by opening the Photos app, tapping the Menu button, then Settings, then Auto Backup, and turn the switch to Off.
To delete the Auto Backup folder, you need to go to your Google+ webpage on a computer, go to the Photos section, select More, and then Albums, and then look for the Auto Backup folder there.