First... Go to customize like you would for the layout you have now, change your settings to the following;
That...will lead you to a page that has four tabs at the top like so;
Tamper with all the settings until you have them to your liking. Then... click 'Save' on any of the pages;
You're done if you DON'T want a header... keeping reading if you do
That... will lead you back to this wonderful page;
Scroll... down to this and click;
Click... to edit your layers;
Go to... and make settings match. Click 'Create' when done;
Find... the layer that you just created and click 'Edit';
Name... the layer; layerinfo "type" = "theme"; layerinfo "name" = "ADD NAME HERE";
Then... underneather that add this, only change 'URL OF HEADER' to the actual URL of your header; function page_layout(Page p) { var string title = $p->title(); """