[ovirt-users] Migrate running hosts to new Engine

Hello all, I need to migrate 4 hosts running CentOS with oVirt 4.2 to a new Engine that runs 4.3 and not disrupt the VMs on these hosts? The VMs need to be running, i have a slim option of downtime for them, but rather not. The reason is that my current engine 4.2 will not upgrade to 4.3, tried so many times, but all i get is a white page after the upgrade, according to engine-setup, was a success. So, how can i do this? Reagrds Magnus Isaksson