Can I update someone's else's phone using my Mac?

[tardman91]

My cousin is visiting and her phone still has iOS 7 and she wants 8. She hasn't been able to upgrade because of space issues and doesn't sync with a computer (and is very tech un-savy). I wanted to use my computer but don't want to accidentally overwrite all of her pictures and videos and stuff. I tried searching but found mixed answers as to whether it would work or not, most of them older results. I haven't even tried plugging it in yet for fear it might start erasing and syncing. Just curious.

 

[spl19]

Connect the phone and cancel all the sync....then update with ipsw downloaded with click+shift and when it will restart unplug it

 

[Givmeabrek]

In iTunes select Edit, Preferences, Devices and check the option to prevent iPods, iPhones, and iPads from syncing automatically. Then you can plug in your phone without any risk.

 

[Jessica Lares]

You don't need to do anything. Plug it in, update it, and it won't sync because the library isn't the same as what's on iTunes.

The syncing automatically option is to stop your own devices from doing so. But these are the ones with the same libraries.