From BlenderWiki

Size and Position

Showing/Hiding the header

Click the small gray triangle attached to the header itself.

(to be written)

Resizing the header

Click and drag the small gray triangle attached to the header itself:

• Dragging toward the center of the Window enlarge the header
• Dragging toward the outside of the Window shrink the header
  • Dragging enough makes the header disappear (same effect of clicking the triangle)

(to be written)

Moving the header contents

MMB-Drag left-right.
Note that if a header has enough room to show all its content you cannot move it

(to be written)