Although there are many topics on this topic but i did not find a one simple straigng forward answers, many just say look at this post or just see how to overrids.
Can you please let me know a simple and straingt forward method or answer how to change the data format
In current versions the date format is set in your Joomla language files, if I recall correctly, DATE_FORMAT_LC1 and DATE_FORMAT_LC2 are used in orders.
Good description of howto in http://forum.joomla.org/viewtopic.php?f=615&t=775861
If you add the overrides for the administrator language file then you can select to add to BE and FE at the same time.
Thanks, I know how to change the LC1 and LC 2 , but is this necessary to override files if so how to do that? If i just change LC1 and LC2 will this work
If you don't set up overrides then next time you update Joomla you will lose the changes. In that thread I linked to it tells you how to do the overrides!
Also see http://forum.virtuemart.net/index.php?topic=113895.0
Dates in front end order display use the language constant DATE_FORMAT_LC4.