Update Hypervisor Hosts from 3.6 to 4

We updated the manager to 4 and after putting the host into maintaince mode we should be able to update the host to version 4.

The problem is that the upgrade button is greyed out.

How can i do the update from version RHEV Hypervisor - 7.2 - 20160413.0.el7ev to RHVH version 4?