If you want to update your phone to the latest Stock ROM you have a couple of options. The easiest way is to see if you can update it with the OTA app (over the air) that is included on your phone. Check->Menu->Settings->About Phone->Software Upgrade. If it doesn’t work you can try Samsung KIES from Samsung (which most likely will not work atleast never for me). If none of those options work or if you want to update your ROM to the latest Unbranded Rom, you may follow this guide. As usual, I don’t take responsibility if you break anything. Also keep in mind that you might loose your guarantee.
sammobile.com is a good place to find the latest Samsung ROM Leaks for various Samsung Phones. If you want to download the latest version for your phone you will most likely find it there. Go to Firmware -> Firmwares -> Type:Smartphone ->OS:Android-> Model:i9100 Choose your region. To download you will have to register for free.
It’s fun to have the latest ROM and a lot of other reasons like it’s better and stuff.. and because you can.
Download Odin 3 v1.85 (simple google search and you should be able to find it or a later version) and then download the ROM from sammobile as explained above and extract the files from the archive.
Power off your phone and then power it on again by holding the following 3 buttons simultaneously.
Volume-Down + Home (middle button) + Powerbutton. If you did it right you should find your self on a screen with the title ODIN MODE and the option of restarting or continue. Press Volume-Up to continue.
Now connect the USB-Cable to your phone. Windows should now try to install the drivers for you phone, just let it finnish. If the driver install fails you should check Samsungs support pages for the drivers to your phone. If it works, Odin should look like this:
Now add the appropriate files to flash as following:
PDA = point to the file with “CODE” in the name
PHONE = “MODEM”
CSC = “CSC”
Make sure only Auto Reboot and optionally. F.Reset Time are checked
Click Start and wait until you see a green PASS on the screen, your phone should now reboot and you’re good to go!