On most devices, you can set your phone to automatically delete messages after a certain amount of time or when storage begins to fill up. This helps ensure that you don't leave sensitive information in your messages for long periods of time.
By default, Android’s Messages app deletes messages after a certain number are stored on your phone. If you’re using Hangouts for text messaging, you can set it to delete old messages once the storage fills up.
1. Open your Hangouts app
This is the app you use for text messaging. If you use the Messages app for text messaging instead of the Hangouts app, your messages are deleted by default.
2. Select “Settings”
You can find this option by tapping the the three-dots icon in the top right corner.
3. Choose “SMS”
4. Toggle “Delete old message” on
If the toggle is on, your messages will be deleted once the storage begins filling up. When the toggle is off, your messages won’t be deleted automatically.