Because you are changing page alignment, you'll want this page to be its own section. We've discussed sections before.
Sections / Headers and Footers in Microsoft Word 2007-2010

If you go to the above chapter and search for alignment you'll find step-by-step instructions.

Briefly, on the Page Layout tab use the dialog box drop down in the Page Setup group. Click on the tab at the top for Layout. The vertical alignment is in the middle of the dialog box.

Note, be careful with this. There have been many postings on forums like this from people who can't figure out how to turn this setting off when it is set by accident (as in copied something from another document).