log out to switch to Unity-2D

[Lenny]

Hi,
I downloaded another copy of Ubuntu 12.04, and it booted up.
So much for the torrents being more reliable.
I have never had a bad download using my browser's download option, but 
yesterday I downloaded 12.04 with a torrent, and although I got it fast, it 
must have been corrupt.
Anyway, in 12.04, I haven't found a way to log out, the power button does 
not offer that as an option, and alt + F1 does not give me a menu.
I want to log out to try to switch to Unity-2D.
Thanks for any help.
Glenn