How to close COM object in VBA code???

[Jojo]

I have a COM server object . It is been used in a VBA code like the
following:

Dim xxx As MyServer
set xxx = new MyServer

MyServer.exe has a main form and when this form closes, it cleans up
the memory. How can I close xxx so it will clean up the memory also?
I tried:
set xxx= nothing
It closes the MyServer application but it does not clean up the
memory. It basically does not call
~MyServer()

Thanks for your help!