Can't find this window!

[sgcrain]

Hi All,
I'm a fairly new Mac user and I'm trying to change the iMessage account
on my 2009 MacBook Pro. I've found answers to this issue on this forum they
they have shown screenshots of this window but for the life of me I can't find it anywhere! Is this window not in Mountain Lion or am I missing something?
Can someone please direct me here? Thanks! (please see the attached image)

 

[thirdeyeopen666]

Open Messages, and either hit CMD-comma or go to the Messages menu and select System Preferences. Then click the Accounts tab.