/For=ForVolumeSpec /Oldest /Quiet %1 %2 /Shadow=ShadowId /Quiet %1 %2 /All - For the given ForVolumeSpec deletes all matching ...

%1 %2 /For=ForVolumeSpec [/Oldest] [/Quiet]
%1 %2 /Shadow=ShadowId [/Quiet]
%1 %2 /All
    - For the given ForVolumeSpec deletes all matching shadow copies.  
    If /Oldest is given, the oldest shadow copy on the volume is deleted
    If /All is given, then all shadow copies on all volumes that can be 
    deleted will be deleted.  If /Shadow=ShadowId is given, the shadow copy 
    with that Shadow Copy ID will be deleted.  Only shadow copies that have 
    the ClientAccessible type can be deleted.
    - The Shadow Copy ID can be obtained by using the List Shadows command.
    When entering a Shadow Copy ID, it must be in the following format:
       {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} 
    where the X's are hexadecimal characters.  This ID can be obtained 
    through the List Shadows command.

    Example Usage:  vssadmin Delete Shadows /For=C: /Oldest