Detailed steps:
1. Download the file attached in this post and copy it into your external SD card
2. Switch off your phone and boot into recovery by holding Volume Up + Power + Home buttons (Stock recovery is able to flash this file)
3. Navigate by pressing the Volume Up/Down button and choose "Apply update from external storage" by using the Power button.
4. Select the file UPDATE-Kinguser-3.4.0.zip
5. The phone will auto reboot and gives root access
6. To check root access download and install Root Checker from Google Play Store.