Cant allocate 700GB of memory on my HHD

[Derpyfickle]

As you see I cant allocate the 700GB and extend it and add that missing memory to my C drive I don't understand why or how to do it if i'm missing anything. Anyways I cant figure it out can any of you?
Setup

EVGA GTX 1070 FTW 8GB
INTEL I5-4690K Overclocked @ 4.00GHz
16GB OF VENGEANCE DDR3 RAM
CORSAIR 350D CASE
Motherboard Asus MAXIMUS GENE VII
Corsair H80I WATER COOLER
CORSAIR 750M PSU
Windows 10 Home
Westren Digital HDD 3 TB
SSD Samsung 230GB
Main Monitor ASUS VG248QE 1920X1080P-144HZ
ASUS VS228 1920X1080P-60HZ
Corsair RGB strafe
LOGITECH G502 MOUSE
Corsair RGB Void Headset

- Thanks,
Cameron

 

[Doseq]

Try to extend partition with Partition wizard.
https://www.partitionwizard.com/

 

[Derpyfickle]

Try to extend partition with Partition wizard.
https://www.partitionwizard.com/

Not working still

 

[SkyNetRising]

Your disk is in MBR format. You can't use more that 2TB on MBR disk.
To use rest of that unallocated space, you'll need to convert your disk to GPT format.

Unfortunately conversion process MBR->GPT is data destructive.
You have to:
backup data from your 3TB drive,
delete all partitions,
convert disk to GPT,
restore your data.

And that's not all. You can boot from GPT disk only in UEFI boot mode.
That means:
your system must support UEFI boot,
BIOS must be configured accordingly and
you'll have to reinstall windows.

So - do you think it is worth to reclaim those 746GB of space?