How can i unregister dll?

I am trying to learn ATL&COM using a book named "ATL Developer's Guide"
The chapter two has a project.
The code like this .

; Server.def : Declares the module parameters for the DLL.
;
LIBRARY      "SERVER"
DESCRIPTION  'SERVER Windows Dynamic Link Library'
EXPORTS
    ; Explicit exports can go here
    DllGetClassObject   PRIVATE
    DllCanUnloadNow     PRIVATE
    DllRegisterServer   PRIVATE

I had registered the dll successfully. But When I try to unregister it , the exception tell me
"The module E:\Server.dll was loaded but the entry-point DllUnregisterServer was not found.Make sure that E:\Server.dll is a valid DLL or OCX file and then try again "

I already used OleView checking the dll .
How can i unregister the dll?
thanks.

Tags: C++, ATL, COM