Upgrading older Spreadsheets to new Google Sheets
This post is from Google Support. For additional information, visit Google Support.
Using the new version of Google sheets will soon be the only way to create and edit spreadsheets. To make sure that everyone can take advantage of all the features available in Sheets, all spreadsheets created in the old version of Google Sheets are being migrated to the new version. This process will take place over the course of 2014-2015.