Firstly, u have to flash TWRP recovery vai CWM recovery. To do so:
1. First download TWRP zip from here:
https://drive.google.com/open?id=0B9xfAoE6jPEBRmFDY1FMdHc1RUk
2. copy it to ur sdcard.
3. Reboot ur phone to CWM recovery and select Install zip from sdcard.
4. Select the TWRP zip and Flash it.
Now reboot ur phone n just after samsung logo appears take out ur battery.
Boot ur phone in recovery mode. Now ur phone will have TWRP recovery.

After this follow the instructions given by Nico. :good: