How do i merge hard disks and then split them to bigger size?

Image: http://www.dodaj.rs/f/19/ag/2iEr6zge/slika1.jpg I want to merge C: (windows and all other stuff) with empty D: so I could make C(200gb) and the rest D: disk. I watched some tutorials here and I tried them but it just got unallocated so I can not expand C: an then shrink it to get new D: disk. P.S. I do not now how to make an backup disk, so if I need to make it write how that one...