Today i will show a short snippet to change the letter from a drive (Volume) using the WMI. the key is use the Win32_Volume class and set the value of the DriveLetter property. this property is read/write so we can update directly the value and then call the Put_ method of the SWbemObject object.

Check out this sample project

{$APPTYPE CONSOLE}

uses
  SysUtils,
  ActiveX,
  ComObj;

procedure  ChangeDriveLetter(OldDrive,NewDrive:Char);
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObjectSet: OLEVariant;
  FWbemObject   : OLEVariant;
  oEnum         : IEnumvariant;
  iValue        : LongWord;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObjectSet:= FWMIService.ExecQuery(Format('SELECT * FROM Win32_Volume Where DriveLetter=%s',[QuotedStr(OldDrive+':')]),'WQL',0);
  oEnum         := IUnknown(FWbemObjectSet._NewEnum) as IEnumVariant;
  if oEnum.Next(1, FWbemObject, iValue) = 0 then
  begin
    //Assign the New letter
    FWbemObject.DriveLetter:=NewDrive+':';
    //Apply the changes
    FWbemObject.Put_();
  end;
end;

begin
 try
    CoInitialize(nil);
    try
      //This will change the letter of the drive E to Z
      ChangeDriveLetter('E','Z');
      Readln;
    finally
      CoUninitialize;
    end;
 except
    on E:Exception do
    begin
        Writeln(E.Classname, ':', E.Message);
        Readln;
    end;
  end;
end.