For images that are already in your catalog, you can select them in the Library module and choose Library>Previews>Build Smart Previews. In that same menu there’s also a choice to Discard Smart Previews. This can be useful if you no longer need to have smart previews for a group of images and you want to reduce the file size of the smart previews cache file.

This Tip originally published in the Tips & Tricks column by Seán Duggan, in Issue 26 of Lightroom Magazine.