I have split my C:\ physical disk into 3 seperate partitions: C, H, and K.

C has my original OS and is the active partition, H has another OS (dual boot), and K has song files.

I want to keep the other OS (Windows Server) and when I am in this OS, I can't delete C ("Windows cannot format this partition").

What is the best way for me to get rid of C, keep all the songs intact, and the Server OS partition, so I replace C with another OS, and then get rid of the original Windows Server OS (So revert the dual boot to a single boot).