Does m_pMyObj = NULL; is the same as delete(m_pMyObj )?

Hello all
I need at some point to clear the class instance created im doing it from outside the class with this method:

void MyObj::ClearInstance()
{
  m_pMyObj = NULL;
}

My question is do I cause memory leak here?
Do I need to delete this instance also or instead?

Assuming this is C++, then the answer is maybe. It depends entirely what type the variable is. Some types do have overloaded assignments that do allocate/delete or AddRef/Release as appropriate (eg ATL).