Well, this one is not so difficult as it seems to be. Just follow the below steps and leave the phone alone, connected to the PC for 30 minutes. You can easily and safely upgrade your firmware version Android Froyo 2.2 to Gingerbread 2.3.6.
This is for the official upgrade which was pushed via Samsung Kies. So, there is no need to root your phone, and it will still stay rooted after the upgrade as well.
So, let’s start.
Step 1 : Backup
1. My upgrade experience proved that you won’t lose any existing data in the phone including the applications after the upgrade, if you do it correctly. But, to be on the safer side, its always a good idea to take backup of the files and contents in the phone before we start to play with it.
2. So, take backup of your Contacts, Memo, Calendar and media files using Samsung Kies.
3. Take backup of SMS using the application SMS Backup & Restore.
4. Take backup of all the Call Logs using the application Call Logs Backup & Restore.
5. Note down the GPRS and other internet Access Point setting details.
Step 2 : Preparation
1. Enable USB Debugging in the phone (Settings — Applications — Development — USB Debugging).
2. You can keep the sim card and SD card in the phone itself as I did, but again, to be safe, remove both SIM and SD cards from the phone, as both are not required anyway for the upgrade process.
3. Connect the phone to the PC.
4. Copy, Export and Backup all the required data to the PC.
5. You may be asked to upgrade the version of Kies itself before proceeding with the firmware upgrade. So make sure there is no such messages.
6. Make sure the PC is connected to internet and is working fine.
7. Charge the phone to atleast 80% in order to avoid the phone from getting switched off during the upgrade process.
Step 3 : Upgrade
1. When you connect the phone and start Kies, you will get a message saying that a new firmware version is available to be upgraded for the phone. Once you make sure that all the data are safely copied, click on Upgrade.
2.Keep the phone connected to the PC and don’t let it get disconnected at any stage of the process.
3. Kies will download the firmware files and the phone will restart and go into Downloading state automatically during the process.
4. The process will take upto 30 minutes depending on the internet connection speed and will display a message once the upgrade is over.
5. As instructed on screen, disconnect the phone and reboot it. You will be able to see changes in the icons already.
6. Re-insert the SIM and SD cards.
7. Connect the phone back to the PC and make sure everything is fine.
That’s it. You can goto Settings — About Phone — Android Version and confirm the version as 2.3.6
Let me know if you are still having doubts or have faced any issues after following the above steps.