check item in popupmenu

Question

i call popumemu(list of checkboxes in another program) using code like:

PostMessage(Wnd,WM_RBUTTONDOWN,0,0x0);
PostMessage(Wnd,WM_RBUTTONUP,0,0x0);

and i can get the HWND of popupmenu window

how to check(uncheck) item at certain item? without sending code:

    SendMessage( TMP,WM_KEYDOWN, VK_DOWN, 0);
    SendMessage( TMP,WM_KEYUP, VK_DOWN, 0);

    SendMessage( TMP,WM_KEYDOWN, VK_RETURN, 0);
    SendMessage( TMP,WM_KEYUP, VK_RETURN, 0);

or there is another way to call popupmenu and check its item?