Theme Tester plugin allow you to change your themes without having the theme visible to your site visitors. The Theme Tester plugin insert a new menu item into your Appearance menu bar which lets the administrator choose to activate theme testing.  Once activated a new page is linked from the Design page where you can activate the test. Then you can change themes as many times as you want without affecting what themes your regular visitors see. Theme Tester plugin is perfect for developing a new theme without disturbing the old one.

Download Theme Tester plugin here.