Proxmox 3.1 - how change master node

I had used two identical PC as a cluster. PC1 (=Master) and PC2 (=Slave)




now I add two other computer (PC3 and PC4) to the cluster.

PC1 = Intel Core 2 with 8 GB RAM (Master)
PC2 = Intel Core 2 with 8 GB RAM
PC3 = XEON with 24 GB RAM
PC4 = XEON with 24 GB RAM

can that work?
I can't migrate VMs from PC1 or PC2 to PC3 or PC4. They do not start. why is that?

How can I migrate the MASTER from PC1 to PC3 or PC4?
I want PC1 and PC2 remove from the cluster.

thx
KWechselberger