You don't say much in your question to explain what you are wanting to ask but I'm assuming you want to update your device and presently have iOS 4.3 on it.
If you device will support a more recent version of the iOS you must use iTunes on the computer you normally sync with. Start iTunes on the computer, connect your device, select your device in iTunes, select Summary from the row of tabs presented and then scroll down under Summary to find Check for Updates.
Your device will be updated to the most recent version of iOS that you device will run on. The current version of iOS is 6.1