Cannot utilise or Extend extra 700gb of 3TB HDD

I have a 3TB WD HDD.

But my C:\ Drive is only 2tb and I have another 746.52GB of of unallocated space.

I have tried to convert my drive to GPT to see if this works but can't, It's greyed out and in DISKPART I get an error "The operation is not allowed on a disk that contains a pagefile volume."

I am running Windows 8.1 Pro 64bit

Attached some images showing the issues.