How do I update my iPhone 5 ios?
From the Settings on your iPhone 5 you can check for updates:


Select Settings [The app that looks like gears]
Tap General
Tap Software Update and follow the instructions.


Alternatively, and preferably, you should use iTunes on your Mac or PC to first back up your iPhone then install the updates.


Plug your iPhone into your Mac or PC using the USB Cable that came with your iPhone.  This is the cable you use to charge your iPhone with.
Follow the instructions presented in iTunes.