Dismounting a VHD volume means removing the letter assignment for this volume.
To remove an existing drive letter from a volume, follow the instructions below.
1. Launch the R1Soft Hyper-V VHD Explorer.
2. Select an attached VHD in the "Attached VHDs" pane.
3. In the right pane, right-click a volume contained in a mounted VHD. Select the "Dismount" option from the appeared menu.
4. Confirm your request to dismount the Volume by clicking "Yes" in the appeared popup.
5. The drive letter is removed from the Volume that you specified.