Historically, the easiest way to update Cisco UCS CIMC firmware has been to load the update ISO in the KVM virtual media, reboot the server and check off the updates required. As Flash has been discontinued, folks can no longer login to the CIMC and access KVM. The only official workaround is to perform a dd copy from a supported Linux distribution with a custom bash script to a USB drive.
Fortunately, there is a much easier workaround that involves using your CIMC login credentials to download the JNLP file required for KVM. Enter the following into your browser:
By doing so, this will download the JNLP file and allow you to access the KVM without having to actually log into the CIMC Flash interface. I'd suggest updating as soon as possible, the HTML5 client is excellent. Unfortunately, the UCS M3 CIMC will always be Flash based, but the same workaround can be used to access the KVM.