Extending my C:\

I have a server I bought from Dell a few years back. I wanted a RAID 5 but for some reason they sent it with 4 Disks (RAID 5) and only 12 GB of space for my C:\ (D:\ is the RAID-5 438GB)

All are basic disks. Needless to say I need to extend my C:\ as it’s almost full.

What’s the best way to go about this? I can’t extend it because there is no more unallocated space and it’s a system boot disk. I ordered a new 160GB disk I wanted to add. Is there a third party solution anyone know of? Any help would be apprciated. Thanks.