In this particular instance this not may not apply, but before expanding a lun you need to be aware of the maximum sizes that the OS can see. While it is possible to create a single lun using all of the space in your array, it most likely cannot be seen by a host. I have seen where customers have an existing lun and expanded it well beyond what the OS can see, which makes a very bad situation.  Seeing your host sees the space as unallocated, your probably fine. Just posting this for other forum readers to consider before expanding.
I have recently opened up some free space on my Clariion CX300 and have added my available LUN to a MetaLUN.  The Server I am using this MetaLUN on is Windows Server 2003.  How would I go about expanding the partition to take advantage of the new space?  The LUN shows up on the server fine and it registers in Disk Management as unallocated space.  I need to keep the existing data on the MetaLUN.  I just need to add to it. 
Expand MetaLUN Partition