Now Turn Off your phone and wait for complete shut down.
then press and hold power+home key+volume down and the same time. and confirm download mode by pressing volume up key.
now open odin and unzip the firmware you download above.
select firmware file in pda and start flash.
After complete install you phone will automatically restart . now continue to install cwm mode.
Download cwm18.104.22.168 from here.
Install Cwm same as you flash the stock rom above. and continue to install gapps.
Download and copy it to phone. turn off your phone and press home+volume up+ power at the same time for a while your start the cwm like below.
now select the install zip from sd card and choose the downloaded file