This is what you need before execution
1. Odin : http://gestyy.com/qMI4lk
2. Stock ROM : http://gestyy.com/qMI2X0
Step :
Open setting on your phone.
Then go to about phone - software info. And tap build version 8 times to activate developers option.
Back to setting, scroll down then open developer options.
Make sure to check usb debugging.
Go to Download mode by pressing volume down + home + power (turn off your phone before)
Then, connect your phone and your pc using usb cable. I recommend use original usb.
After that, open odin. And click on AP tab then browse the rom files.
Click Start :)