If you are selling your old Android phone, do remember to remove all the files before selling it. There are several ways to delete files but here is on way to remove them easily.
Step-by-Step Guide to Delete All Files on Android Phone:
Factory reset can erase all your data. You might want to back up and double check important files. Basically, videos, notes and pictures are worth saving, while other files can be restored by the Google Play Store.
1. Open Settings in the Notification bar or choose the Menu button and click System Settings or Settings.
2. Select Personal or Security and then click Backup and Reset, then choose Factory Data Reset.
3. Confirm deletion. All your apps, system settings, Google account, pictures and other files will be deleted.
4. Remove the microSD card with the photos and keep it for use in your new device.
5. Check the battery status. It should be at least 50% full. Then select Reset Phone. Once the device deletes all data and information, reboot it in its factory settings.
6. Turn off your device, remove the SIM card before selling it away.