Make a back up. Grab a copy of RSD Lite 4.9. Im sure u can get it at 4shared. Or just Google it.
To SBF
Put .596 SBF file on your desktop.
Grab RSD Lite 4.9 and install it. Once installed open it.
Power off your phone. Hold camera button and Vol DOWN button together. While doing that, tap your power button until the bootloader screen comes up and says connect device.
Connect your phone to your pc via USB
U can click show device to make sure RSD Lite sees it. (may take a few tries)
Select the .596 sbf file on your desktop
Click start
You know your done when the device reboots. Might take a while. If you bootloop, just battery pull and repeat process. When its done you'll be back at the activation screen and you'll be on stock non rooted .596 which then you can go to System Update and grab .602