You should have OpenManage Server Administrator installed ... you can check it there (Storage, PERC, Virtual Disks). Assuming your drives are larger than 40GB and that you have a second partition on the "disk", the only thing you can do (aside from paying a lot of money to do it for you) is to backup the D: drive, delete it, extend C:, recreate the D: drive, then restore data to the new smaller D: drive.
The C drive on my Dell power edge T620 currently has 40 GB and is running low on disk space. Is it possible to add another hard drive to the raid to extend the C drive?  Is it possible to determine what raid configuration it has from windows 2008 r2 server or do i need to shutdown the server and boot it to see the raid configuration?
Adding disk space to power edge T620 C:/ Drive