Server 2008 partitions on large HDD array

Dear experts.

We're setting up a series of new HP DL380 servers for general use, all running Windows 2008 R2.

The server is populated with 6 x 2Tb SATA disks all set up in a single RAID 5 array.   We set a system partition of 70gb and nothing else, looking to create the rest of the partitions in Windows Storage Manager.   Installation has gone fine and lovely.  However, Windows Storage is seeing the disks space as:

C:  70gb NTFS  Healthy.     1978.00GB Unallocated.     7266.93GB Unallocated.

Normally, within Windows I delete any non unnecessary partitions and create an extended partition of all the space then create logical partitions inside.  However, right clicking these two partitions allows me just a Simple Volume on the 1978GB and nothing at all on the 7266GB.   Eventually I want 4 x 1.9Tb and 1 x 1.3Tb.

I've been reading up on MBR limitations and it seems I need to use UEFI but this is a new one on me and I cant find any info on converting or installing it from scratch.

Any advice?

Thanks
Paul.