How do I install iOS 14.8 and iPad 14.8

You can read about how to update your iOS or iPadOS device to 14.8 by following the directions here: Update your iPhone, iPad, or iPod touch - Apple Support. If your device does not have enough storage space to download the update, you can connect it to your computer and update using the Finder (macOS Catalina or later) or iTunes (macOS Mojave and earlier or Windows).

If your signature is correct and you own iPhone 5s, you cannot update to iOS 14.8. Your phone is 8 years old, too underpowered and lacks the hardware required to run anything higher than iOS 12.5.4.

You don't say which model iPad you own, but if your iPad is stuck on iOS 12.5.4 or lower, it too would be too old and lacking the hardware to update further.

If you need the newer iOS versions, it is time to move up to newer, more modern devices at this point.