You will need to do the following...
1. Make sure you have Fastboot installed in your computer which is part of the Android SDK. Install appropriate drivers if you need to. Instructions all can be found at the Android SDK Google page.
2. Take the contents of the factory image you downloaded as I suggested above and extract them to your " /platform-tools/ " directory inside your Android SDK on your hard drive using 7zip or WinRAR.
I based the instructions/filenames using the Gingerbread v2.3.6 factory images, adjust if necessary for ICS 4.0.4
The files you need from inside the factory image zip file are below.
(Inside the image-soju-grk39f.zip)
3. Boot into your bootloader (Press Power + Volume Up) from a powered off state. Now unlock your bootloader if you haven't already done so. Connect you device via USB cable to your computer. Open a Command Terminal Window and type in the following below.
4. From the bootloader screen once again Open a new Command Terminal Window and type in the following...
fastboot oem unlock
: Optional :
fastboot flash bootloader bootloader-crespo-i9020xxka3.img
fastboot flash radio radio-crespo-i9020xxka3.img
fastboot flash boot boot.img
fastboot flash recovery recovery.img
fastboot flash system system.img
fastboot flash userdata userdata.img
If you choose to relock your bootloader after your finished, from the Terminal Command Window type the following code
Then reboot the device.