To free the assigned drive-letter again use the subst command like this:Subst x: C:\Very\Long\Folder\Path
Note when restarting the computer then all mapped drive letters are forgotten. One can put the subst command into a startup-script which is launched at startup, so the mapping is done automatically again at user login.Subst x: /D
Note the utility Visual Subst is a more GUI friendly utility for managing virtual drives created with subst (Has option to mount drives at boot / startup).
Note Windows Vista User Account Protection introduces a special behavior with Subst.exe as the drive-letter is only seen by the user-account that has performed the mapping. This means that when changing between regular user and elevated user then, one has to perform the subst command in both contexts.
Credits SearchWinComputing.com
Visual Subst: Be nice if a name could be substituted for the default. When I use it I get the drive letter, but it's name is that of the host drive.