First off, let’s see the products that are compatible with this software update. Apple claims that the supported devices are the iPhone 3G, iPhone 3GS, iPhone 4, iPod touch 2nd generation, and iPod touch 3rd generation (late 2009 models with 32GB or 64GB).
Some iOS 4-specific features are unavailable with older devices. For example, Multitasking, Bluetooth keyboard support, Home screen wallpaper, and Data protection are not available for the iPhone 3G. They are, however, for the iPhone 3GS. A complete list of iOS 4 specifics (including full changelog) is provided here. Now, let’s move on to the steps iPhone and iPod touch users need to take to start enjoying these new additions.
Downloading and Installing iOS 4 for the iPhone, iPod touch
(The steps described below apply for both iPhone and iPod touch devices)
1- Get the latest version of iTunes to your computer;
Download iTunes for Mac (Free)
Download iTunes for Windows (Free)
2- Launch iTunes and connect your device to your computer;
3- Select your device in the Source List on the left, under Devices;
4- At this point, iTunes should detect that iOS 4 is available for your “supported” device. If not, hit the “Check for Update” button.
5- iTunes will notify you that a new version of the iPhone operating system is available for download. Accept it by clicking “Download and Install;”
6- Allow iTunes to perform the software update for your device.
IMPORTANT: do not disconnect your device until the update has finished! You will know that the update has been successfully applied when the device reboots and shows the iOS 4 home screen.
Although there are more than four steps to follow, Apple summarizes the process of updating your device’s firmware as follows:
You’re now ready to enjoy the new features of iOS 4!
Alternately….Owners of a supported device can also download the iOS 4 update / restore IPSW file to their computer and put the update process on hold. Direct download links from Apple’s servers are available by going here - Download iOS 4 for iPhone and iPod touch (Free).
When they are ready to update, users can fire up iTunes with the device connected, select their device, click “Restore” with ALT (option key) held down, select the iOS 4 IPSW firmware bundle, and click “Choose.” The installation process will begin, with the same rules being applied - do not disconnect until the update is finished.