IF YOU HAVE REALLY MESSED UP A PAGE, and accidentally saved it, simply click on the history tab (at the top) and then click on the date immediately preceding that of your change, then click on edit this page, then save the resulting page. This will revert the change.
IF YOU HAVE REALLY MESSED UP A PAGE, and accidentally saved it, simply click on the history tab (at the top) and then click on the date immediately preceding that of your change, then click on edit this page, then save the resulting page. This will revert the change.