Most computer monitors are now widescreen and your older presentation should be updated to display properly so your presentations are not boxed with large black margins
In PowerPoint, you can convert your old presentations to wide screen format by going to the Design tab, slide side and choosing Widescreen.
In Google Slides, you can convert your old presentations to wide screen format by going to File >Page Setup.
However, you will notice that you may need to adjust positioning of each item on each slide and resize graphics that have been stretched. You can scale up high resolution images to fill up your slide and add background images to help fill the extra space on your wider presentation.
|Google resource on how to modify slide size for your Google slide presentation: https://support.google.com/docs/answer/|
MS Office resource on how to modify slide size for your PowerPoint presentation: https://support.office.com/en-us/article/