Pre Upgrade Instructions:
So, first up before proceeding to update, you need to ensure that you have synced all your contacts with your Google Account, all sms, applications, videos and music files which are there in your phone should be taken a backup or else the data will be lost. Anything which is in SD card will not be lost, so you can alternatively move to SD Card.
Next up remove the SIM card as well as the external SD cards if any in your phone, just to make sure that in an unlikely event the data in it doesn’t get corrupted,
Ensure that you have kept original USB cable handy which you have got with your Galaxy S GT I9000 and also the Galaxy S device,
Additionally, ensure that your phone has at least more than 50% of battery power left, this is just an advisory which if followed then you will not experience any difficulties as while updating of the device the battery consumption is at a maximum,
Ensure that your computer / laptop which runs on a XP, Vista or Windows 7 OS the firewall and other antivirus programs are disabled and also you should have admin privileges to download and install the software including the drivers and also along with this you will be requiring the USB port on your computer which supports USB 2.0.
(Optional) Many of the Galaxy S users have reported the problem that they are unable to get into the download mode which is the top most necessity for updating your device, so for all those we came up with a tutorial here, just follow the given instructions and you can easily fix the download mode and also the recovery mode bug. This procedure is only for those whose devices unable to get into the download mode and the recovery mode.
Please note that flashing with the firmwares doesn’t mean that you are ROOTING your device. If you have flashed with Voodoo Lag fixes then too you can easily flash your device with this firmware.
8. Ensure that you have closed the KIES completely and also disable any firewalls, antivirus if any.