How do I unmaximize full screen view in virt-manager?

Neither of the existing answers worked for me when running a VM in fullscreen using 12.04.

If you look at the top center of the screen, you can see a little sliver of white. Hover the mouse over that sliver and it will reveal two icons: an "unfullscreen" on the left, and a "send key combo" on the right. You may have to ungrab by pressing Ctrl-Alt momentarily before it will come up. Click the "unfullscreen" to get back to a windowed view.

Ctrl+Alt+F Is the toggle switch for the top center menu bar.

If you see no menu bar in the top center after a slight over

Toggle it on with

Ctrl+Alt+F

And try again

When in full screen mode, hit Ctrl+Alt to 'unhinge' the mouse and move the mouse to the top-middle of the screen. A little applet drops down to allow you to leave full screen and send key-combinations.