How do I delete my backup, and how long is it kept?

Go to Settings → Account. Tap one device's backup to delete just that one, or tap Delete Backup to delete every device's backup; both also turn off backup on this phone, and they're gone from the server right away. Other devices with backup on back up again the next time they're opened, or within about 20 minutes while they're open. Turning off Back Up to WitnessWork asks whether to delete this phone's backup too. A device's backup that hasn't been updated for 400 days is deleted automatically. Delete My Buddies Data (Buddies Settings) also deletes your backup, because it gives you a new account and recovery key; with backup on, the next backup goes to your new account. If deleting fails because you're offline, nothing changes; try again when you're connected.