If you go back to Insert | Page Number and choose a different option, it
should move it for you.

Alternatively, View | Header/Footer.  Delete the existing number--there is
probably a little gray box around it (a frame), be sure to delete that too.
Put the cursor wherever you want the number (if you hit tab one, it will
take you to the center, tab twice will right-align), and hit the # icon on
the header/footer toolbar.