Disk Director 11 and 3 TB Hard Drive

I have a 3TB Hard Drive (Seagate Barracuda) which I initialised with MBR and only about 2 TB is available. The first 454.0 GB (primary), (292.9 GB unused) is my C drive under Windows 8, and the second drive is 1.557 TB (logical), (1.233 TB unused) and is my H drive.
Clearly I made a mistake in not initialising using the GPT file system, and now I need to recover from that mistake so that I can use all the 3 TB on the disk which is showing as 2.729 TB Basic MBR.
Can I do so without losing the data on either of the drives (C & H)?
If so what do I do, in what order, and how.
If not, then what can I do so that I don't lose my Windows 8 installation on the C drive? (I can copy my data on the H drive to another drive if necessary, but there is nowhere to which I can clone the C drive.