Use the show upgrade_history command to display the software upgrade history.
None
EWC.extremenetworks.com# show upgrade_history Date Type Version Thu Feb 24 11:41:00 EST 2011 Upgraded 07.41.01.0150 Tue Jan 11 10:36:44 EST 2011 Installed 07.41.01.0100T Tue Jan 11 10:36:27 EST 2011 Installed OS-7_41_0-7