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.
As of the time of this answer's writing (July 2019), Ordinal Scale is available both subtitled and dubbed on Hulu in the U.S., as well as on Steam (because Steam has anime for some reason).