Hi early1945, the option is presented when saving to Flickr, but there is currently a bug which is stopping the option from displaying.
This should be fixed within the next few days, but in the meantime you can workaround the problem by disconnecting and reconnecting to Flickr. You can do this on the Library tab by clicking Options under your Flickr account name and then disconnect. Then click the red connect button again. When you save to Flickr the replace option will appear.
