Sword Art Online the movie Ordinal Scale has already been released according to Wikipedia, but I can't find it anywhere. So where can I watch and download legally.
You can't, the only place you can see it at the moment is in a theatre, as it hasn't been released on disc yet. Once it releases on disc, you can then either buy it from a shop or use a legal streaming service like Netflix if it gets released there. TV channel also play anime sometimes, so you might be able to find it there too soon.