On the Design tab of the Ribbon, locate Slide Size in the Customize group, near the far right end of the toolbar. Select Slide Size, and then select either Standard (4:3) or Widescreen (16:9). When PowerPoint is unable to automatically scale your content, it prompts you with two options:

Change the slide size. On the Design tab, in the Customize group at the far-right end, click Slide Size. Click Custom Slide Size. In the Slides sized for list, click the size you want to use, or use the Width and Height boxes to select custom sizes. Click OK.

You can change the slide size and orientation, set the paper size for printed slides, and edit headers and footers from Page Setup in PowerPoint 2016 for Mac.

In PowerPoint for the web, you can do basic background formatting of one or more slides with a solid color or a picture. To do more advanced formatting, such as adding a color gradient or making a picture transparent, use the desktop version of PowerPoint on Windows or macOS.

Arrange slide content with different PowerPoint slide layouts to suit your taste and preference, or to improve the clarity and readability of the content. Select the slide that you want to change the layout for.

If the file size of your presentation is too large, try the following tips to make it more manageable.

Change the page orientation in your PowerPoint presentation to landscape or portrait layout. Select Design. Select Slide Size > Custom Slide Size. Select Portrait > OK. In the next dialog box, you can: Select Maximize to take full advantage of the space available. Select Ensure Fit to make sure your content fits on the vertical page. Want more?

On the Design tab, select Slide Size, and then Custom Slide Size. Under Number slides from, select the up or down arrow to switch to the number that you want to start from:

Click the Design tab of the toolbar ribbon, and then, near the right end, click Slide Size. On the Slide Size menu that appears, select Custom Slide Size. The Slide Size dialog box opens. In the Slide Size dialog box, select Portrait, and then select OK.

To set a custom size, including width, height, slide numbering, and orientation of slides and notes, click Custom Slide Size on the Slide Size menu. To make sure your slides will print the way you want, preview your handouts before printing.