Formatting (or reinstalling) Samsung Galaxy S2 I have some experience about Android phones (but i'm not an expert) .

I have problems with my Samsung Galaxy S2 (GT-I9100) . Its battery heating too much, there are a lots of applications, sometimes phone freezing and not responsing, it's battery consumption is too much and it's a little slow. And sometimes restarting itself.

In shortly, i'm using it for long time, i installed too many apps and uninstall some of them. Now i want to clear everything (except SD card datas) , delete all datas / apps . And start from origin, again. I'll my (really needed) applications from Google Play, later.

In computer knowledge, it's mean format , i think.

But for mobile phones, I'm not sure, it's called as "formatting" or "firmware reinstalling" . 

I plugged my phone to computer and launch Samsung Kies but there isn't reinstall firmware option. 

Notes


Android version : 4.0.3
My phone isn't rooted. (and i won't do that)
I'm worring about warranty. So, please just legal methods.
I don't want to lose my datas (music, etc) on my SD CARD.
I don't want to send my phone to technical service for this. It'll take at least 4-5 days.
What you are most likely look for is called "factory reset". As the name suggests, a "factory reset" is supposed to reset the device to its original state, as it was delivered by the factory. What in fact is done by a factory reset is to wipe all user-installed apps and all user data (for the latter, except data stored on sdcard).

This can be done either from within the system menu (look for the entry with the "fence" symbol, it's labeled something with "Privacy") -- or using the hardware buttons, as described at Hard-Reset.Com:


switch off your phone
press and hold volume-up and home buttons
press the power button for 2-3 seconds
release only power button, but KEEP pressing Volume up + Home Buttons
with Volume down select wipe data/factory reset (3rd) > Press Power


There's no need to re-install any firmware. The system resides on its own (read-only) partition, which is not touched by this process. Having followed above steps, your phone should then boot in a clean state. Don't worry if the first boot after that takes a bit longer -- that is fully normal. Also this does not void your warranty, as these steps would also be recommended by the service hotline if your device went nuts, and they want to eliminate the cause of misconfiguration or misbehaving (user-installed) apps.

For a reference, you might also want to take a look at the question Do a total wipe of my device.