How to upgrade official firmware on Samsung Galaxy S II I9100

If you are a new user of Samsung Galaxy S II I9100 and you wanted to upgrade your phone's firmware to any latest updates, all you need is a personal computer or laptop and install a software program called KIES, you can download it via Samsung official support.
You can't do it over the air or OTA like any other android smartphones by using software update option, Yes you can see a software update option in phone under settings and you need to specify your samsung account details as well.. but  as of now its doesn't work on Samsung Galaxy S II I9100.

Aside from Kies update you can also manually upgrade the device by a way of using ODIN downloader tool and an original firmware.

This method is  not recommended for beginners since it will cause some problems and sometimes mess up the phone, called bricking.

If you want to learn by this method you may visit XDA-developer, many advance users in there shares a useful tweaks and tips about Samsung Galaxy S II I900 firmware.