frame navigation in WPF

You can use the VisualTreeHelper class to find the Frame that contains the Page and, set the Source property of the Frame to the new Page.

You can implement the Click event-handler of your Button, as the following:

private void btnChangePage_Click(object sender, RoutedEventArgs e)
{
    // Find the frame.
    Frame pageFrame = null;
    DependencyObject currParent = VisualTreeHelper.GetParent(this);
    while (currParent != null && pageFrame == null)
    {
        pageFrame = currParent as Frame;
        currParent = VisualTreeHelper.GetParent(currParent);
    }

    // Change the page of the frame.
    if (pageFrame != null)
    {
        pageFrame.Source = new Uri("Page2.xaml", UriKind.Relative);
    }
}