It is really easy to update your iOS software, but to prevent data loss in case something goes wrong it is important to first create a backup of your data. Please read the article “Backing up the device via iTunes or iCloud” if you do not know how to do that.
With iOS 5.0 there are now two different ways to update a device, the usual way via iTunes and an “Over the Air” update that does not require you to connect your device to iTunes. If you have not yet at least iOS 5.0 the update can only be done via iTunes.
1. Update via iTunes
Before you do the update, back up your device, make sure to transfer your purchases and sync your device one last time.
And then click on your device in the sidebar and choose “Check for Update” (or “Update”) if iTunes already knows that there is a new update available”.
From there on you only have to follow the instructions from iTunes.
After the update has completed everything should be as it was before. If that is, due to some reason, not the case, just restore your device from the backup and everything will be fine. You can find out how to do that in the article: “Backing up the device via iTunes or iCloud”.
2. Over the Air update
With iOS 5.0 it is possible to update without having to plug in your device. Make sure you have a recent backup and that your device has at least 50% battery power left.
Then on your device, go to Settings andthere choose “General”, then “Software Update”.
Your device will check if there is a new update available. If that is the case, just follow the instructions.To do an over the air update the device has to be connected to the Internet via Wi-Fi.