To change the default color palette in Powerpoint double click on the color swatches and select the colors you want. The color swatches is on the "Home" ribbon.
Open PowerPoint, you should be able to see a tool bar with the following: Home, Insert, Design, Animations, Slideshow, Review, View. Click on Design. This will cause the options underneath to show different slideshow set ups. Near the far right, there is an option titled 'Colors'. If you click on the down arrow, you can choose a different color palette.
On "Format" menu, click "Slide Color Scheme". In the "Standard" color palette tab, click the color scheme you want, then click "Apply" to apply to selected slides only. Click "Apply to all" to apply to entire presentation. Click "Custom" tab to customize the colors of various components on slide.
To change the color pallet in Powerpoint, select the range of the colors you wish to change and right click. Select Font and select the default color you wish to change it to.