Greetings.
You basically boot a HUU ISO just like as if you were doing an upgrade.
You'll probably get an extra prompt to confirm you actually want to downgrade.
You do need to make sure your versions you are downgrading to, still support all the hardware involved.
The various HUU release notes can be found at https://www.cisco.com/c/en/us/support/servers-unified-computing/ucs-c-series-integrated-management-controller/products-release-notes-list.html
Some of them do contain specific notes about upgrade/downgrade dependancies.
Actual HUU ISO upgrade process is listed at https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c/sw/lomug/2-0-x/3_0/b_huu_3_0_1/b_huu_2_0_13_chapter_011.html
Also, make sure your OS drivers match the HCL at https://ucshcltool.cloudapps.cisco.com/public/#
Why are you wanting to downgrade?
Thanks,
Kirk...
