As of 20 15.9, the highest version of ios is 8.4.
The operation of the Apple 5 upgrade system is as follows:
Step 1: Log in to Apple official website, download itunes software, install it and open it.
Step 2: Connect Apple 5 and the computer with a data cable.
Step 3: In the summary interface, click "Check for updates" and follow the instructions of itunes to upgrade the system version.