Best way to remove LUNs from ESXi 4.1??

I know that KB 1015084 discusses unpresenting a LUN containing a datastore  from an ESX/ESXi 4.x host without removing the contents of the  datastore.

What's the appropriate procedure for removing LUNs if:

a) I've moved ALL the VMs off the LUN to other storage (e.g. DAS, NFS) ??

b) the SAN will have its controllers replaced (MSA 2012i G1 upgrade to P2000 G3 controllers)??

Thank you, Tom