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.
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.