WARNING! When you factory reset your phone, all personal data stored on the internal memory will be deleted, including ringtones and other media files, downloaded content, contacts etc. Furthermore, by resetting your phone, all settings will be restored to factory values.

NOTE: Before you reset the phone you can visit this thread for a guide on how to back up data on the Galaxy A3. You can also visit this other thread for instructions on how you can restore data.

Factory Reset via Settings:

1. Open the apps drawer and go to “Settings”
2. Scroll to “Personal” and tap “Backup and reset”
3. Optionally, you can enable or disable "Back up my data” and “Restore”
4. Tap “Factory data reset”
5. Tap “Reset device” and if your phone is lock screen-protected, enter the PIN / password to proceed
6. Tap “Continue” > “Delete all”

Factory Reset via Recovery:

NOTE: If you are unable to reset the phone using the method above, you should be able to reset it from the Recovery menu. Recovery can be accessed by performing a specific combination of button presses, as follows:

1. First, make sure the phone is turned off
2. Next, press & hold “Power”, “Home”, and “Volume Up” at the same time
3. When the “Samsung” logo appears, release “Power”
4. At the “Android” logo, release the other two buttons, and wait for the “Android system recovery” menu to appear
5. In the Recovery menu, press “Volume down” repeatedly to navigate to and highlight “Wipe data / factory reset”
6. Press “Power” to select the highlighted option
7. Highlight “Yes – delete all user data” and press “Power”
8. Wait for the phone to reset. Once done “Reboot system now” should be highlighted
9. Press “Power” to reboot your phone

Check for OS Updates:

NOTE: After you factory reset your phone you should check if new OS updates are available for download. To do this:

1. Tap “Apps” on the home screen
2. Open “Settings”
3. Swipe to “System”
4. Tap “About device” and check if a new update is available for download
5. If an update is available, follow the on-screen prompts to install it