As far as I know you can't - when I got mine I had to use the cd that came in the box. However I believe that the only difference between the UK and the American sony library software is that the uk software sends you to Waterstones to buy books and the American one allows you to access the Sony online bookstore, although if I'm wrong about that I hope someone corrects me.
Some people from the UK have the American library software so that they can use the Sony store, as Waterstones can be accessed via the web.
If you want the American software it's available
here.