Samsung has begun distributing the Android 4.1.2 update OTA across the globe for a little while now. But if you haven't received your update and are getting a little impatient, you can install it right now using the Flash program "Odin," which is not at all difficult to use.
To snag Android 4.1.2 on your Galaxy S2, first you'll need to install Odin and Samsung's stock ROM (international version). Sammobile offers both as downloads, but because it can be painfully slow to download them from their site, we're offering them to you on our servers as well. Here you can download Samsung's stock ROM, and here you can download Odin. Obligatory warning: AndroidPIT cannot be held responsible if you follow our instructions incorrectly and end up damaging your phone.
Here's How to Install The Update on Your Galaxy S2:
1. Download Odin and the firmware on your PC (links above) and extract the files, placing them in the folder of your choice.
2. Secure your smartphone with Ultimate Backup because you are going to need to return your phone to factory settings and clear all caches. Theoretically, it's possible to install the update without wiping your device, but there's risk that your phone then won't run smoothly.
3. Turn off your device. Then start it in recovery mode by holding the volume up, home button and power button simultaneously until a small green Android appears with a menu above him.
4. Use the volume buttons to choos "wipe data / factory reset" and select it with the power button. Scroll down to "yes" using the volume button and select it with the power button again. Then repeat the procedure with "wipe cache partition."
5. Choose "reboot system now" using the power button.
6. Turn the phone off again.
7. Restart phone in download mode (home + power + volume down).
8. Start Odin on your computer
9. Click PDA and add the unzipped firmware code: I9100XWLS8_I9100XXLS8_I9100FOPLS3_HOME.tar.md5 to PDA
Leave everything else unchanged and make sure that the "repartition" box is not checked.
10. Connect your Galaxy S2 to your PC via USB cable. In the top left of Odin, you should now see a box which reads 0:COM 12 (It may also read a different number besides 12).
11.Click "start" and wait until the green "PASS!" button appears. Wait until your Galaxy S2 has restarted before you disconnect it.
12. THAT'S IT!
If your phone gets stuck during the boot process, do not panic! This often happens during the Flash process. Try pressing the power button down until the Galaxy S2 turns off, then repeat steps 2 through 4..