How to upgrade to latest iOS for my iPhone, iPod or iPad?

It’s easy. Just 3 steps. Here’s the guide:

Step 1: Connect iPhone to computer
 
Before it, Make sure you have the latest version of iTunes. The latest version of iTunes can be downloaded from http://wwwitunescomdownload.com/itunes-download or official website: http://www.itunes.com/download.

Step 2: Open iTunes

Open iTunes, Then select your iPhone under Devices in the Source List on the left panel.

Step 3: Start Updating

In the iPhone summary panel, click "Check for Update" button.

Then the update confirm dialog will open. Click "Download and Install".

Don’t disconnect your iPhone from computer and just wait for 2-3 minustes, The latest iOS will be downloaded and updated.

Now your iPhone is running with latest iOS. Just enjoy the new features!

iOS 4.0 is the latest version of firmware for iPhone. It brings some fantansy features:

• FaceTime.
  Finanlly, you can video call your friends with iPhone. With just a tap, You can share your smile to the whole world via Wi-FI with FaceTime.
   
• Multitasking.
  With the revolution iOS 4 multitasking, You can run your favorite apps in background and switch between them in seconds.
   
• HD Video Recording.
  iOS 4 support 720 video recording now.
• Folders for Apps.
  It’s a new way to organize your apps. You can create a folder an move many related apps into it. Is it your iPhone more clear now?
  

Where to manual download iOS 4?

Here are url list to download it:

iOS 4 for iPhone 4:
http://appldnld.apple.com/iPhone4/061-7380.20100621,Vfgb5/iPhone3,1_4.0_8A293_Restore.ipsw

iOS 4 for iPhone 3GS:
http://appldnld.apple.com/iPhone4/061-7437.20100621.5urG8/iPhone2,1_4.0_8A293_Restore.ipsw

iOS 4 for iPhone 3G:
http://appldnld.apple.com/iPhone4/061-7436.20100621.58Yt4/iPhone1,2_4.0_8A293_Restore.ipsw

iOS 4 for iPod Touch 3rd Generation:
http://appldnld.apple.com/iPhone4/061-7381.20100621.AzSP9/iPod3,1_4.0_8A293_Restore.ipsw

iOS 4 for iPod Touch 2nd Generation:
http://appldnld.apple.com/iPhone4/061-7435.20100621.tr49t/iPod2,1_4.0_8A293_Restore.ipsw

Now, You can enjoy your iPhone or iPod touch with latest revolution features from Apple!

The only change in iOS 4.0.1 update package is "formula to determine how many bars of signal strength to display".

iOS is Apple’s mobile operating system developed originally for the iPhone, and later deployed on the iPod Touch and iPad  as well.  The latest version of iOS is 4.0.1.

iTunes is the interface to manage contents of iPod, iPhone and iPad. It can be downloaded from here: http://www.itunes.com/download.