2
The date format can be changed in languages/yourlang/global.php, way down at the bottom of the file.
If you want to change your header, all you have to do is thange the correct theme.html (located in your themes/themename/theme.html). Changes need to propagate so maybe your browser cache is keeping it 'old'. Also, check the update templates setting in the system admin -> prefer3ences -> general settings page.
Herko