|Are you saying the CD drive is not showing up in Disk Management? Expand disk management to full screen. The CD may be at the bottom.|
To change those drive letters first assign a higher drive letter to the CD (removable storage) drive. Then assign the letter D to the second hard drive. After that, E will be available for assignment to the CD drive.
If the CD drive truly is not showing in Disk Management then you may have 2 drives on an IDE cable that are jumpered wrong. Use Master for one and Slave for the other. Western Digital hard drives have a second Master setting which is Master alone. That is only used if that is the only drive on that cable.