Android Update for Galaxy S I9000
Samsung Kies kept failing on me when wanting to update from 2.3.3
by saying no new update exists(!), and Samsung Support could not offer
any help. So I ended up uninstalling Kies entirely and rather spent a few
hours learning how to do it myself instead. I got a hold of the latest
official firmware, as well as a copy of Odin3 - the "Internal Samsung
Engineer flashing software". Both things can be downloaded from the
XDA forums

Start by leaving the phone unplugged from the computer, and make sure the battery is fully charged in advance.
Update procedure
1) Download firmware, in my case I downloaded I9000XWJVZ|2.3.6|OXA|November 2011. (OXA = Open Europe).
2) Download Odin3 and start it.
3) Select the PDA file = CODE_I9000XWJVZ_CL762604_REV03_user_low_ship.tar
4) Select the PHONE file = MODEM_I9000XXJVT_REV_00_CL1064602.tar
5) Select the CSC file = GT-I9000-CSC-HOME-MULTI-OXAJVT.tar
6) Shut off your phone and start it again by pressing Volume down + Home + Power button.
7) Your phone should start in download mode, you can now connect the USB cable.
Odin3 should show this when your phone has been properly connected (at least 1 yellow ID:COM):

8) Press START. Odin3 should show this when it's done:

9) Let the phone reboot entirely before removing the USB cable.
Your phone is now upgraded!
10) It's RECOMMENDED but not required to perform a proper hard reset afterwards, to avoid
conflicts from the different versions and get a clean system. Turn the phone on with
Volume up + Home + Power button and choose "wipe data/factory reset"
(If you used a PIT file, this step is not necessary).
Why did I not use a PIT file?
Because there's no need to re-partition unless your current
partition table is giving you problems. If it does, experiment with the 512, 513 and 803. The
only main difference is some scaling of space being done between the user and system partitions (10-20 MB).
This document was last updated December 13th, 2011.