IOS 4.1

So you need an IOS of 4.1 to access achievments, what is it and how do i get it to 4.1?!

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1.To upgrade your iPhone or iPod Touch to Apple's iOS 4.1 firmware, make sure you're running the latest version of iTunes on your computer.
2.
Once you've made sure iTunes is up to date, connect your iPhone or iPod Touch to your computer using the included USB cable. If iTunes doesn't launch automatically, you'll need to launch it manually.
3.Once iTunes is open, and your device is connected, select your device in the iTunes sidebar so that the summary page (shown here) is visible. Take notice of the button for Check for Update but don't click it quite yet
4.Just to be safe, make a backup of your settings prior to upgrading the firmware. To do this, right-click on the device icon in the iTunes sidebar and select Back Up. It should only take a minute to create a backup, and it's time well-spent. If anything goes awry during your iOS update, you can use this same menu to select the Restore from Backup option.
5.Finally, click the Check for Update/Update button from the device summary page. If your iPhone or iPod Touch is compatible with iOS 4.1, iTunes will tell you that an update is available for download and will guide you through the installation.

iOS 4.1 is a newer version of operating system for your idevice.

Upgrade your device by opening iTunes on pc with idevice plugged in. Then click on device. Next click check for updates and follow apples instructions.

Edit: great instructions Ahmedb

Oh well thatz much better than my description lolz
EDIT: O-mazing description ahmeb

Thx Ryan.