Hard Reset for Sony Xperia GX SO-04D
In order to hard reset a Sony Xperia GX SO-04D, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Sony Xperia GX SO-04D device will be brought back to the default configuration of a brand new device.
1. Download and install PC Companion. Open it.
2. Window below should appear.
3. Select Start.
4. Allow the installation process to complete.
5. Accept the Phone / Tablet Software Update and select start.
6. Continue to repair my phone / tablet, confirm the oncoming instructions and read the Important Information.
7. A preparing computer for software update window will open. 
8. Select the phone / tablet model. Follow the on-screen instructions that will appear.
9. Done!