They are not installed by default - you have to check a box at the time of installation to have them installed. You should be able to go to the Windows Control Panel, Programs and Features (or whatever this is called in your version of Windows) and find AutoCAD Architecture 2013. Right click it and choose Uninstall/Change. This should open up the Setup dialog for ACA 2013. You should have an option to Add or Remove Features; choose this and add the Express Tools.
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