All settings in Page Setup, including page orientation, can be applied to
either the whole document or specific section(s).  You can either insert a
section break manually by clicking at the top of the second page and going
to Insert>Break>Next Page>OK, then go to File>PageSetup and change the
orientation (by default, Apply to will be "This Section").  Alternatively,
you can select all the text of the either the first or second page,
whichever you need to change the orientation of, and go to File>PageSetup.
Change the orientation, and make sure that Apply to is set to "Selected
Text".  Word will automatically insert any needed section breaks in order to
apply the new PageSetup settings to the selected text only.

Regards,
Chad DeMeyer