Remove disk drives ?

Scenario  EV 9.0 / Win2K8

Had a mount point for Indexes. Two attached LUNs. Was running low on space.  Attached a new LUN, copied data from both old LUNs, changed drive letter for old mount point, added old index drive letter to new LUN (no longer using mount points for indexes).

This process has worked, new index volume is being utilised.

Went to offline the old LUNs for deletion and EV shutdown.  How can I remove these old LUNs ?

ps I'm am positive I have done this before - just can't seem to find the info on the forum.

Thanks