Locale and time zone information for a Google Apps Spreadsheet can be changed using the Spreadsheet settings. Launch a new or an existing Spreadsheet and then navigate to File menu. Select Spreadsheet settings from the list of available menus.
This would display the following Spreadsheet Settings window.
You can change Locale and Time Zone using the respective dropdown that are available. After making the necessary changes, click the Save settings button to confirm and save the changes.