How to migrate iOS to iTunes | How to confirm backup or update iPhone , iPod in iOS , iTunes without erase data

iOS is a rich features technology an easy-to-use interface, amazing features, and rock-solid stability, and it is the foundation of iPhone. And even as other phones try to catch up, the technologies and features built into iOS 4 keep it years ahead of the competition.
You can use iTunes as the alternate to update or restore iPhone or iPod software. Apple recommends updating iPhone or iPod touch to use the latest software. You can also restore the software, which puts iPhone or iPod touch back to its factory condition.
Normally if you attempt to update, the iPhone or iPod software can updated but your settings and media are not affected. If your device currently has a software version prior(higher to lower) to 2.0 (1.x) and you are updating to software version 2.0 or later, all data on your device will be deleted in order to perform install the new software.
In this situation, iTunes will offer you to create a one-time media backup of your device depending on what content is on your device and what content is stored in the iTunes Library you are connected to.
You have to ensure that you have enough free space on your Mac or PC to accommodate a backup that matches the capacity of your iPhone or iPod (32 GB, 16 GB, 8 GB, or 4 GB) if you proceed with the this backup.
If you choose to restore option, all data is erased/deleted from iPhone or iPod, including videos,songs, contacts numbers or contact person, calendar information, photos and any other data. All iPhone or iPod settings are restored to their factory condition.
iOS features an amazing features, easy-to-use interface, and rock-solid stability, and it is the basement of iPhone.

How to restore your iPhone / update /iPod using the downloaded IPSW file:
Free download the firmware for your device
OPTION-click (on Macs) or SHIFT-click (on PCs) on the Update / Restore button in iTunes
Now you will be able to inform iTunes to use the IPSW file you downloaded to update or restore your iPhone or iPod
Note: To be able to download iPhone/iPod firmware directly from Apple you will have to follow these steps:
You have to ensure you are using iTunes 8. Connect your iPhone to your computer.
When your iTunes opens, select your iPhone under Devices in the Source List on the left.
From your iPhone Summary pane, click Check for Update.
Click Download and Install. Do not disconnect your iPhone until the update has completed.
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