I have created a page view which contains files listing. On existing Page there are three tabs called 'thumbnails' 'files' and 'thumbnail plus' now I want to override on 'files' tab view with my page view. How do I do that?
Just set the path of the view to the same as the path of the page you want to override.
That's all you need to do, paths that Views takes care of "win" over paths provided by core and other modules. The most famous example of this is probably the taxonomy/term/% page View that comes with the module. Once enabled, term pages aren't handled by core any more, the View takes their place.