Replacing slides

In order to reduce the amount of flickering and shimmering caused by my pan & zooms, I want to replace all my (100+) images with lower res versions. I don’t really want to start from scratch, as I’ve spent a long time setting everything up. What’s the best way of replacing the slides please? Is it File/Replace Media File for each one- or is it easier to use the placeholder feature and drag the lower res files over the originals?

Thanks very much

Looks like click and drag works!