The semi-automatic way: Upgrading your Android device's OS is easy. This is because your carrier automatically sends you the latest updates so sooner or later you'll get an over the air update to the latest supported Android OS. All you will need to do is confirm the installation and let it go. Once installed, you can confirm by going to your phone's device information screen to see that the latest version of Android is now on the phone. * Note: It's always a good idea to back up your phone first, just in case, and to plug in your phone via USB or AC adapter during the upgrade. The last thing anyone wants is for their update to go bad because the phone battery died. On some Samsung devices, you'll need to enable your Samsung account in order to update to Android 3.2. To do so, go to Settings > Accounts & Sync > Add account > Samsung Account > You will then be prompted to set up a Samsung account, which requires inputting your email and creating a password. Now to rooting proper!
The Semi-Manual way: You could decide to search for the latest OS yourself just in case there's a delayed notification to your device. Do this by:
pressing the 'Home' key
Next, press the 'Menu' button and go to the 'Settings' option.
In settings, you'll see the option 'About phone' near the bottom, select 'System updates'
Your phone will look for any new Android updates to download and install.
To streamline this process, download the app ANYCUT and you can create a shortcut on your main screen which will do all that with a quick tap.
The Manual way If your phone is too old, your carrier doesn't think you should get a particular OS, or you're just too impatient to get it, you can always 'root' your phone and download a custom ROM of that given OS once it becomes available. Rooting means you get administrator access to your phone and can customize it's functions. There is a very active community of Android fans who are constantly working on versions of Android called 'ROMS' which make a new version or Android available to phones that don't get them, or that streamline the OS taking out overlays like Motoblur or TouchWiz.
How to upgrade Android OS with custom ROM Upgrading with a custom ROM that is made from a much more recent version of Android actually means replacing your whole OS with this "new OS". This is recommended especially if you have an older devices that has no chance of getting upgraded again, but you want to squeeze more life out of it before you buy a new one. To update with a custom ROM: