You will need to obtain the required firmware from the Support site (https://support.arubanetworks.com/). When you upgrade the firmware on the controller this will in turn upgrade the firmware on the AP's.
Within the release notes for each firmware there is details on how you can perform a backup and also the upgrade as well.
Note you will need a valid support contract in order to access the Support site.
If you wish to check the ArubaOS version running on your controller/AP, use the following command:
#show version