Default [Q] Swapping ROMs in MultiROM

I have MultiROM installed in my Nexus 4. CM11 is my primary ROM and I have Ubuntu Touch, Firefox OS and OmniROM as secondary RONs. However, I want to ditch CM11 and swap it with OmniROM (so that OmniROM becomes my primary ROM) before removing CM. How do I do it? And how can I do it and carry CM's /data partition to Omni?