You will receive your notification to upgrade once Microsoft can confirm your device is ready to upgrade. Microsoft looks at the specific compatibility for your device and overall demand for Windows 10 when deciding if a device is ready to upgrade.

Before notifying you, Microsoft will download the installation files needed in the background. Then, you will receive a notification on your desktop letting you know that you can upgrade right away or schedule a time that works best for you. Microsoft is rolling things out in phases to manage the high demand, particularly in the first weeks following Windows 10 availability.