Removal of resized images

I believe there are plugins that will remove resizes, but EWWW does not do that (it doesn’t create them in the first place), it merely exposes the fact that they exist, and permits you to disable them in the future.

Once they are removed, and you’ve disabled the ones you don’t want via EWWW, you should be able to regenerate them again with the Regenerate Thumbnails plugin. That should prevent causing problems with existing content, but make sure you do a full backup before you get too far on this.