Ok, that's weird. The button only appears in landscape view. Then it works but is pretty buggy and the map excerpt is very small. So I edited it now as good as it seemed possible. However, in Vespucci there is really no option to change existing data, even my own additions are hardly editable after uploading. And btw in general, what is the meaning of using all those tags if most of them don't get visible on the map?