Choose Application menu→Sheet Setup.
On the Sheet Setup dialog box, click the Background tab.
Select a new background sheet from the list.
Tip:
When you change the background sheet, the size and margins of your working sheet equal the settings of the selected background sheet.
You can double-click a background sheet tab to access the Sheet Setup dialog box, or you can use the shortcut menu. To display the shortcut menu, right-click while the cursor is over a sheet tab.