To do that you will have to install 'GnoMenu' separately from the installed 'ZorinMenu' - it is possible - then right-click the panel at the bottom of the Desktop and select 'Dock preferences', then click on the applets tab - you will need to scroll down the availability of 'GnoMenu after installation and drag it to the 'fake' panel at the bottom of the 'Applets' tab and select the ZorinMenu and click on the up arrow above the fake panel to remove it leaving the GnoMenu applet on the far left.
To install GnoMenu see here:
http://www.upubuntu.com/2012/03/how-to- ... unity.htmlSee it in action here:
http://vimeo.com/85050945