How to flash a new Firmware on Samsung SM-G313HU Galaxy S 3 Duos

In this tutorial you will learn how to Flash a new Firmware on Samsung SM-G313HU or Galaxy S 3 Duos.
Note, that this tutorial will work on other devices too, but you wouldn't find the Firmware in this tutorial, so before starting ask Google for you Firmware.

Watch the Video tutorial from bottom of the article or read the Written tutorial.
1. Install USB driver for Samsung SM-G313HU on your computer.
Download SM-G313HU driver here

2. Activate USB Debugging from Settings > Developer options > USB debugging, if you don't find Developer options under the System tab, you need to activate it.

How to activate Developer options on Samsung
SM-G313HU 
Navigate to Settings > About device > tab Build number several times till a warning message appear stating: Developer options activated

3. On your computer run Odin3, make sure that Auto Reboot and F. Reset Time are checked.
Download Odin3 here

4. In the Files box, click on AP and select your Firmware ISO image, wait till Odin3 loads it. Check the Message box, the final message is "Added".
Download Stock ROM for Samsung SM-G313HU Galaxy S3 DUOS

5. Start your phone in Download Mode.
For this turn off the phone, then press and hold Volume Down + Home + Power keys. Hold them till a warning message appears. Then you need to confirm that you want do download a custom OS pressing Volume up key.

6. Connect your device to the computer through the USB cable and check Odin3. The first rectangle from ID:COM tab should change its color to blue.

7. Press the START button and wait till the process finishes. During the process its normal for the phone to restart several times.

That's all.