You can change your presentation's design at any time by following these steps:
Choose Format, Apply Design Template from the menu to open the Apply Design dialog box.
Select a new design for the presentation.
Click the Apply button. The new design is then applied to every slide in your presentation.
Changing the document's presentation design is similar to changing the layout of an individual slide. When you apply the presentation design's formatting to your presentation, your slides won't lose any text or objects you have entered; however, the formatting may change.