^ Yes and No. On some of my drives it shows up with an assigned drive leters, other it does not.
Be nice to know the sizes of the two partitions.
If you can copy all the files off of the D drive onto a backup drive, you can delete the "D" drive partition and Then use windows disk management to "expand" your C drive to the desired size. then repartition the remainding amount as the "NEW" D-drive.
Unsure, just google expand C drive.