Hello,
if you want to change date format, you can do it in configuration on first Main tab.
There is also small legend how to do it:
Date formating in component and Joomla! too is string consisting of special aliases. For example string %A %e %B %Y formats date 1.1.2011 as Saturday 1 January 2011. To read more about time formating, visit PHP strftime function page. For date formating we recommand use predefined formats. Using custom formats is for advanced users.
Select Use custom formats and create your own dates.