For normal updates, all VMware Appliances have the capability of updating from the CD-ROM attached to the VM. On the download page for vCAC, you'll see an ISO available with "updaterepo" at / near the end. Download that, attach it to the VM, then go to VAMI; under Update -> Settings, change the repository to Use CD-ROM Updates. Then do a check. Should show as available.
-Steve
I have written a blog post for VCAC Appliance, but its pretty much the same steps involved in updating IA.
http://vpirate.in/2014/09/12/vrealize-automation-6-0-1-6-1-part-1-upgrading-vcac-appliance/