You can upgrade to the latest AOS8.x however as part of the upgrade process you will need to factory reset the controller.
At the time of writing the latest AOS8.x release will support your APs.
https://www.arubanetworks.com/en-gb/support-services/end-of-life/
Within the AOS8.x upgrades, there is two "standards" of firmware. Either a Conservative Release (CR) or a Standard Release (SR).
The Conservative Release tag signifies a release has been deployed in multiple customer production networks. Conservative Releases can be considered as the “gold standard” or “go to” releases within the Aruba WLAN portfolio. Aruba recommends the adoption of Conservative Releases in any customer’s production network.
The Standard Release tag signifies a release introducing significant new software features and/or hardware platforms. Any customer interested in benefiting from new software features or hardware platforms are encouraged to upgrade to a Standard Release. Standard Releases always complete a thorough quality assurance and test cycle before posting and becoming available to all customers. After adoption by multiple customers, Standard Releases may be “promoted” to Conservative Releases.