how does iTunes update iPhone on my computer ?

Hello, Salama Ramadan.

Thank you for visiting Apple Support Communities.

Here are the steps on how to update your iPhone via iTunes.

Update your device using iTunes

If you can’t update wirelessly, or if you want to update with iTunes, follow these steps:

1. Install the latest version of iTunes on your computer.
2. Plug in your device to your computer.
3. In iTunes, select your device.
4. In the Summary pane, click Check for Update.
   
5. Click Download and Update.

If you don't have enough free space to update using iTunes, you'll need to delete content manually from your device.

Find out what to do if you get other error messages while updating your device.

Update the iOS software on your iPhone, iPad, and iPod touch

-Jason H.