Close a Qframe when it open new one

[gfxx]

my application have a mainwindow with a full screen mdiarea and a menù bar.

When cliked on menù item it open a qframe/qwidget. Every menù item open a new different qframe. My qframe have different classes but are all parent of qframe.

How I can close a qframe when I open a new one with menù item?

this code, in my mainwindows work only when the old qframe is open one time:

@ void main2::newframe()
{

    if (m_newprogram != NULL)  //work only if m_newprogram is already used
       { m_newprogram->close();}
   m_newframe = new Frame(ui->mdiArea); 
   m_newframe->show();
   m_newframe->activateWindow();
   m_newframe->setAttribute(Qt::WA_DeleteOnClose);

}@

any suggestions?