Yes

Select Yes to overwrite and recreate all existing thumbnails and images. Yes is required if you have changed any thumbnail or image option, like thumbnail width or image border style.

No

Select No to only create thumbnails and images for new and modified original images. No is faster, but keep in mind that you have to overwrite existing thumbnails and images if you changed any thumbnail or image options. If you don't do so, you won't see the changes.

Don't ask again

Check the Don't ask again option if you want to control overwriting images on the File Locations page.