Decide How to Download iOS 12.4.5
Next you'll want to decide how you'll download and install the iOS 12.4.5 update on your device.
If you plan on installing iOS 12.4.5 Over-the-Air (OTA) through the device's Settings, you'll need to have at least a 50% charge and you'll need to be connected to a Wi-Fi network.
You can also install the iOS 12.4.5 update through iTunes if you're running Mojave or older. Simply plug your device in, click the correct device under the Devices tab and check for an update.
If you're running macOS Catalina you'll need to update via Finder, not iTunes.