The WCM keeps track of all previous versions, and can compare the current version of a page to a previous one.
Step 1: To view a page's previous versions, or to rollback to an earlier version, navigate to the page using the Asset Tree and click the "Advanced" tab, then the "Versions" link.
Step 2: The Previous Versions page shows all previous versions of a page. To see what the page looked like at a different point in time, click the linked name of the page.
Step 3: While viewing an older version, the WCM presents quick links to other versions (Older, Newer, Current) and actions that can be performed with the currently viewed version (Activate, Delete, Compare with Current). To rollback to an earlier version, go to the previous version you wish to restore and choose "Activate".