My Aruba S1500-48 switch comes with a very old ArubaOS 126.96.36.199 built on 2013. The latest version as of June 2020 is ArubaOS 188.8.131.52. It's released on Oct 2019. An Aruba account is needed to download.
Once got the upgrade file, go to WebUI (add ip address to browser compatibility view list if your AurbaOS version is low) - Maintenance - Image Management.
Aruba switches come with two partitions, they are separated and can boot from any. Remember always flash image to the one is not in use and switch to it once upgrade is successful.
Switching to the desired partition at Maintenance - Boot Parameters.
The new version of ArubaOS doesn't need browser compatibility view anymore.