After turning on the rendering of page labels, as an alternative to entering the horizontal and vertical margins numerically, you can drag page labels into place when in Annotate mode.
With the page labels showing, activate Annotate mode. The page labels will be framed by a blue box. Drag the box to where you want the labels to be. If for the page where you drag, the label justification is set to center you will only be able to drag vertically.
