Place the insertion point at the end of page 13.
Activate the (Page) Layout tab of the ribbon.
Click on the Breaks button and select Next Page from the dropdown menu.
Activate the header of page 14.
Click to deselect the 'Link to Previous' button in the Navigation group of the Design tab of the ribbon.
Click Previous to go to the header of the first section.
You can now clear this header without affecting that of the second section.