Change the Default Template or Theme in PowerPoint 2010
A theme is a combination of one or more slide layouts with coordinating theme colors, a matching background, theme fonts, and theme effects. PowerPoint provides several standard themes. Find a standard theme that you like, and then modify it by changing the theme colors, theme fonts, or the background. You can then save the file as a custom theme. Once you create a custom theme in PowerPoint, you can use it in other Office applications.
How to apply a theme to PowerPoint presentation - YouTube
However, there are a few factors to consider when choosing a theme PowerPoint. The purpose of the presentation will dictate the type of theme PowerPoint needs to use. A slideshow intended for a staff meeting can be slightly more informal or playful than a business proposal for a potential client. Then, the content also plays an important role. For example, it is not unusual for cosmetics or fashion companies to use light colors and playful themes, which would be inappropriate in the case of a construction company. Finally, simplicity is always a safe bet, as a busy theme PowerPoint presentation can be distracting.