[ovirt-users] upgrading hardware node

I already upgraded ovirt management engine from 3.6.3 to 3.6.4. Now I want to upgrade the hardware nodes. I see there is a "Upgrade" button on the Hosts tab but I have not found any way to make it enabled. Even with host in maintenance it still is disabled. How do I get that to work? I'm sure I could just run yum update, but aren't you suppose to be able to do it in the GUI? Thanks.