Here is another quick fix for PowerPoint files that may have grown too large and sluggish due to all the snazzy imported images and graphics. The change in file size can be dramatic, depending on the images.

• Right-click any picture in your presentation and select Format picture from the
  drop-down menu.
• Under the Picture tab, click on the Compress button.

• The Compress Pictures menu is shown above. Under Apply to, select either Selected pictures or All pictures in document.
• Under Change resolution. select Web/Screen if your presentation will be used for a screenshow. Select Print if you plan to pass out your presentation in printed form.
• Under Options, select both Compress pictures and Delete cropped areas of pictures.
• Click OK.
• If you get a Compress Pictures warning, select Apply.
• Save the presentation under a new file name (just to be safe).