Yes... you can update the Samsung Galaxy S phones just like any other Android phone by getting the update.zip file from somewhere, putting it on your SD card, booting into recovery mode, and flashing the update.
Where to get the update from? I have no idea... try the xda-developer forums.
How to get it on your SD card without a PC? You should be able to download the zip directly onto your phone using the browser. You will then need to use a file manager (although I think your phone comes with one called My Files) to rename the file to update.zip and move it out of the Downloads folder into the root folder (i.e. the top folder, not a folder called root lol).
To boot into recovery, I believe you turn your phone off, hold the volume down button (or up?), the Home button, and the power button, all at the same time for ages while the phone boots up. Maybe Google this to find out what the key combination is for your specific phone. It takes like 10 tries to get it right too.