The iOS 17 file size will be several gigabytes, and if you're running out of storage, you'll need to clear some room before you can download and install iOS 17. You won't be able to download iOS 17 using your mobile data, so connect to a stable Wi-Fi network before starting the installation. Even if you're plugged in, the battery needs to be over 20% to install iOS 17.
You won't be able to download iOS 17 if you're under 50% battery, so it's safest to plug in your phone while you update. Make sure your iPhone is connected to power.
