[Q] How to update Samsung Galaxy SI9000 from rooted android 2.2 to newer version?

Hi,

A friend of mine rooted my samsung mobile Galaxy S I9000 with a android 2.2 version. I cannot contact him anymore to help me with the update and I am really a newbie in this rooting world. So, I am coming on this forum to have some advice. I read information on rooting your device, in which everything is explained very well, but could not find information on how to update once a device was rooted (probably I did not search in the right place). What I did so far is:
1) Taking backup of my pics (by manually drag and drop the folder on my pc), SMS and call logs (with sms backup + app), syncronized my contacts with gmail so that I can recover them later on and backup the music folder. I installed backup Titanium to back up my apps on my SD card.

But now, I am stuck with some questions (could you guide me where to find the information?):
1) Which most recent version of Android is supported on the device I have?
2) Is there important information that I forgot to back up?
3) Is there a guide with step by step procedure on which files I have to download on my pc and which procedure to follow? Or could you advice me some useful links?

thanks!