Can I change the tile of DEFAULT back button of navigation bar

Answer 1

yes, from the parent view controller (the one above the one where you want to change the title), add the following:

self.navigationItem.backBarButtonItem.title = @"Your Title Here";

Answer 2

This can be done by simply setting the title of the parent view controller:

If a custom bar button item is not specified by either of the view controllers, a default back button is used and its title is set to the value of the title property of the previous view controller—that is, the view controller one level down on the stack. (If there is only one view controller on the navigation stack, no back button is displayed.)

UINavigationController Class Reference