Well I've imagined, perhaps naively, that it will sit in whatever folder you have designated as your 'Downloads' folder, until such time as you open the file and click 'install' - much the same as any other program.

But if I were you, I'd make sure to take a full system back-up before close of play on 28/7/15.

As there's a window of one year from 29/7/15 in which you can get the free upgrade, I've decided not to 'register' in advance, and to leave it six months until it's been running in the real world and, hopefully, the major crap has been sorted out.