In several weeks, Google will begin auto-migrating spreadsheets created prior to December 2013 (including any subsequent copies) to the new Google Sheets. Users of these older sheets will see a notification before the migration process begins. No action is required as a result of the auto-migration and no data should be affected. However, in a few cases, the result of some formulas and other features may be slightly different in the new Google Sheets. See the article "What's different in the new Sheets?" in the Help Center for detailed information.