If you need to restore a previous version of a page, click Previous Versions in the Page tab at the top of the page. You ...

If you need to restore a previous version of a page, click Previous Versions in the Page tab at the top of the page. You can then click on any of the versions in the quick launch to view the page as it existed at that time. If you want to restore to a version, select it and click Restore this version in the toolbar.