Changing paper size for a complete workbook:

If you need to change the size of paper on which your worksheets will be printed, it can be bothersome to make the change on each worksheet individually. Here's how to make the change on the entire workbook, at one time, regardless of how many worksheets it contains.
1. Right-click any worksheet tab. You'll see a Context menu appear.
2. Choose Select All Sheets. All the worksheet tabs should now be selected.
3. Display the Page Setup dialog box. (In Excel 2007 display the Page Layout tab of the ribbon and click the small icon at the bottom-right of the Page Setup group. In earlier versions of Excel choose File | Page Setup.)
4. Make sure the Page tab is displayed.
5. Using the Paper Size drop-down list, choose A4.
6. Click OK.
7. Right-click any worksheet tab. You'll again see a Context menu.
8. Choose Ungroup Sheets.