I assume we're doing the external interface, and staying in the same subnet so that we don't have to modify the default gateway.
If I were doing it, I think I would first change the VIP address, which is found under Cluster Properties.
Then, under Network Settings, for each cluster member, I'd change the address on the External port (Port 1). I'd have a ping up to the old address and the new address to see that the change had occurred and been recognized.
If the change did not appear to occur, I'd get on the console (I always like to be on the console during a reboot) and reboot the cluster.
You have to break the cluster, change the IP addresses, then re-join the cluster....
I'd make sure I was local to do it though. just in case you can't access the devices after the initial IP change.