How to change date and time format in Zorin OS 6

Use dConf editor.
Goto com > canonical > indicator > appmenu > datetime.

Once in date time, change the value for time-format to custom.
In custom-time-format enter your customized string:

%A, %B %d, %Y  %I:%M %p

%A = Full weekday name
%B = Full month name
%d = Day of month
%Y = Year
%I = Hour in 12h format
%M = Minute (00 - 59)
%p = AM or PM

http://askubuntu.com/questions/43999/how-to-change-the-date-format
http://www.cplusplus.com/reference/clibrary/ctime/strftime/