There is no option to change a file name it just overwrites the original file.
Also the files size option is not available. This is true for stand alone and plugin version
Also not when saving the files. Later to my surprise I found these options again when saving a file
You must open the image from the File Open dialog as it can only offer those options when NOT opened as a plugin. If you use Open in from finder/file manager or any other application it opens as a plugin.