As Zhuge says, it does depend on the API you are using. If you are developing in DirectX then you would use their coding. With Windows API you can use the keybd_event function to maximize the console window. If you want to maximize using the Win32 window, then you would use
ShowWindow(hWnd,SW_MAXIMIZE);
Where hWnd is the declaration you make at the beginning of you window call.
You've got to turn off your window borders, set the topmost property to true, and set the window position to fill the entire display. You can also first list it as maximized so that you can easily restore it.