Pixel size of thumbnails not changing

I have the thumbnails/previews set to be 600 px wide.

But when I download, they are only 400 px wide.

Is there another setting I need to change?

Thanks,

Maureen

The new preview size will only work for new uploads. Already uploaded
images will have the same preview size as when they were uploaded. If you
want to have them in the new size, you will need to reupload.