Hi,
After you connect an additional monitor, you can use theNew Display Detected dialog box to indicate how you want the desktop to appear on the monitor's display.
You can choose to mirror, or duplicate, your desktop on all displays.
A mirrored desktop—the default display option—is useful if you plan to use your mobile PC to give a presentation on a projector or a fixed display in a conference room, such as a wall-mounted plasma display or TV-type monitor.
To change the primary monitor to secondary and secondary to primary, you may follow the steps below and check if you can change it.
a) Open Display Settings by clicking the Start button, clicking Control Panel, clicking Appearance and Personalization, clicking Personalization, and then clicking Display Settings.
b) To designate the primary display, on the Monitor tab, click the icon that corresponds to the monitor that you want to designate as the primary display, and then select the ‘This is my main monitor’ check box.
c) Select the screen resolution and color quality for each monitor that you're using.
I would suggest you to follow the links and check.
http://www.microsoft.com/athome/organization/twomonitors.aspx
Work and play better with multiple monitors http://windows.microsoft.com/en-US/windows7/work-and-play-better-with-multiple-monitors Move windows between multiple monitors
http://windows.microsoft.com/en-US/windows7/Move-windows-between-multiple-monitors