How to change date format in oracle?

ALTER SESSION SET NLS_DATE_FORMAT = 'DD/MM/YYYY hh:mi:ss AM';


Ref links:

http://www.dba-oracle.com/sf_setting_parameters_tips.htm
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:351017764854