In i Tunes, click the phone icon (near the upper-left corner) to bring up the Summary screen for your i Phone.
Then, in the Backups section, click the Back Up Now button.
WARNING: To avoid “Automatic synchronization” of your i Phone, i Pad, or i Pod by i Tunes click and keep the Shift and Ctrl keys pressed while you open i Tunes. To back up i Phone data via i Tunes, open i Tunes and connect your i Device.
Chances are good that it does, and if the i Phone is a 5 or newer, or the i Pad is an Air or Mini 2 or newer, it will be supported.
Only the newest model i Pod touch is supported, however.
An i Phone update will lose contacts on your device.
Many users have this problem, in general, you can backup and then if you lost contacts, you can recover by backup files.
Apple's i OS 10.3 is probably coming by the end of March, bringing with it a batch of updates and new features.
Before you upgrade, however, it's a good idea to make sure you've got a full backup of your i Phone, just in case something goes wrong.
To back up i Phone, i Pad, or i Pod Touch data prior to upgrading to i OS 8, refer to this tutorial: How to back up i Phone data Updating to i OS 8 will restore the i Phone settings to their factory defaults.
Before choosing to upgrade to i OS 8, be also sure to back up your i Phone settings via either i Tunes or i Cloud.
Let’s walk through some important steps to prepare for the i OS 10 update the right way, including checking for supported hardware, doing a little cleanup, insuring adequate backups have been made, and then of course, diving right into the install.