SharePoint 2010 provides a seamless, culture-specific experience that enables site owners to create sites in a specific language and configure the regional settings that are appropriate for those sites.
SharePoint Server 2010 uses the following types of regional settings: locale, time zone, sort order, calendar, and currency. You can specify the locale, sort order, time zone, and calendar settings on the Regional Settings page.
Change Date Format:
1) Go to "Site settings" from "Site Actions" Tab.
2) Under the "Site Administration" Section click on "Regional settings".
3) In "Locale" choice select desire option; example format DD/MM/YYYY you need to select "English (United Kingdom)".