Deleting and adding iSCSI LUNs

I have the following:
ReadyNAS Pro 6
RAIDiator 4.2.27
X-RAID2 with 6 disks
Server 2008R2 with native iSCSI initiator
4 iSCSI drives; E:, F:, G:, H:

PROBLEM:
I no longer use or need E, F & G drives and went to delete these 3 targets on the ReadyNAS. It looks like I can't just delete one drive target because all 4 belong to the same LUN0 and it looks like it is really deleting LUN0, not the individual target drive. Here is the message I get...

"Deletion of the iSCSI LUN 0 device will wipe out all the data residing on it and will remove the iSCSI target device. If you are sure you want to do this, please type DELETE ALL LUNS and click Apply.Enter "DELETE ALL LUNS" if you want to delete all LUNs in this target."

Does anyone know how to delete the 3 targets and leave the 4th target and LUN0? I don't know but I am guessing the second target should have been created on LUN1, third on LUN2 and so one but I did not see a way to select LUN number on a target during a test.

Thanks
Jan