Once you're comparing two presentations, you can review the differences between the two and choose which revisions to keep. After you've reviewed all of the differences, you can then save the approved changes into the open presentation.
Select a change in the Details tab of the Revisions pane.
A box appears on the slide, detailing all the changes to the object or text.
To preview what the slide would look like with the changes accepted, click the Slides tab on the Revisions pane.
Do one of the following:
Accept a change: Select the check box for the change or changes that you want to make.
Reject a change: Do nothing; keep the check box unchecked.
Use the Previous and Next buttons on the Review tab to move through the revisions, accepting or rejecting all of the revisions in the presentation.
Expand the Compare group if necessary.
Click End Review.
You need to verify that you want to end the review and discard any changes you rejected.
The changes from the other presentation are saved into the open one.