Most Pages templates are created for documents with standard paper sizes, but you can change a document’s paper size at any time. You can also change its orientation (portrait or landscape). Afterward, you may need to make adjustments so that the document looks the way you want.
Tap 
, then tap Document Setup.
Tap 
in the top-right corner.
Tap a paper size.
If you don’t see paper sizes, tap the Document tab.
Tap 
to return to Document Setup, then tap Done in the top-left corner to return to the document.
Tap , then tap Document Setup.
Tap in the top-right corner, then tap a page orientation.
You can use only one page orientation for your document. Pages doesn’t support a mix of pages in portrait and landscape in the same document.
Tap to return to Document Setup, then tap Done in the top-left corner to return to the document.
Tap , then tap Document Setup.
Tap in the top-right corner, then tap Custom Sizes.
Tap Width or Height, then change the value to the new size.
To save your changes, tap Done in the window.
Tap to return to Document Setup, then tap Done in the top-left corner to return to the document.