From Microsoft

We want to give every customer a great upgrade experience, so we’re rolling it out in an organized way to manage high demand and to make sure that the upgrade is right for your device. After July 29, when Windows 10 is ready for your device, it will download in the background. You’ll then get a notification to schedule your upgrade right away or at another time that’s convenient for you.

Here are some common questions about the upgrade process. Click on the links for answers.