Change the size of your slides - Microsoft Support
https://support.microsoft.com/en-us/office/change-the-size-of-your-slides-040a811c-be43-40b9-8d04-0de5ed79987e
To change the slide size: Select the Design tab of the toolbar ribbon. Select Slide Size near the far right end of the toolbar. Select Standard (4:3 aspect ratio) or Widescreen (16:9) or Custom Slide Size.
Select the Design tab of the toolbar ribbon.
Select Slide Size near the far right end of the toolbar.
Select Standard (4:3 aspect ratio) or Widescreen (16:9) or Custom Slide Size.
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