You should be able to switch monitors in the settings panel, and reassign the monitors accordingly.
If that doesn't work, you might consider unplugging the monitor and trying to reset the default monitor as the primary panel.
I have an HP pavilion Dv6 laptop with a 1366 x 768 resolution. It boasts to have a 1080p output so i bought a Samsung 2333HD monitor for it to work on my photos. But I connected it today and it looks terrible. I fiddle with the settings but it is stuck on monitor 1 (laptop - but saying it is the samsung monitor) and monitor 2 (samsung but saying it is the laptop. I realise this may not make sense but in short on display settings the monitor 1 (the laptop) has the samsung driver installed and monitor 2 (the samsung monitor) has the laptop driver installed. I cannot for the life of me switch them. Please help!!!