If you’re updating your iPhone or iPad to iOS when it becomes available today, you’ll get better results if you connect to iTunes instead of doing it over the air.
Your iPhone needs somewhere to keep the download until it installs the new software, and that download is several gigabytes. If you download to your computer, you don’t have to start deleting photos of dear Aunt Marge or kitty.
It’s a safe bet that your work or home internet connection is faster than your phone’s is, and if you’re using wifi from your phone, your desktop is probably faster over the same connection. Also, you won’t have to pay data overage charges. Yum.
Finally, don’t forget to back up your iPhone, once you’re plugged in to iTunes anyway. Just in case.