If you still require the ISO for legacy maintenance or a staged migration, 1. Where to Download the Cisco ACS 5.8 ISO

Once logged in, click on the "Support" tab and select "Software Center" from the drop-down menu. In the Software Center, search for "Cisco Access Control System" and select "Cisco ACS 5.8" from the search results.

Allows for programmatic internal user password changes. System & Installation Requirements