change short date format

[nickon2]

Hi,

I am using joomla 2.5.111 and  vm2.0.20b with Greek language and although the long date format is displayed OK the sort date format is displayed like 2013-06-05 (yyyy-mm-dd) but it want it to display like 05-06-2013  (dd-mm-yyyy)

What do I need to change ?

Kind Regards