Click Format > Presentation settings > Change theme. Select the theme you want to use and it's automatically applied to your presentation.
To select your own background image:
- In the presentation editor, select the slide you want to change and click Format > Presentation settings > Change background.
- In the window that appears, click Insert image.
- Click the Choose File button to search for an image.
- Click Save.For best results, use images with an aspect ratio of 4:3 and 800x600 resolution.
- Follow steps 1-3 above to open the Change Background window.
- Click the paint bucket icon below the Insert Image link.
- Select your desired color from the palette.
- Click Save.