@Zoltan - yes, this is a huge component that is missing from Squarespace. I contacted support about this and was told that images that are no longer used on a page will be deleted automatically from the file upload browser after a certain amount of time. And if there is an image or file that needs to be removed immediately, we should contact support and they can help. This workflow is certainly not ideal by any means, but thought it might be helpful to share in the meantime.