If you’ve reserved your Windows 10 upgrade on your Windows 8.1 or 7 PC, but it’s not showing up, this can be because of 2 reasons. If the Windows 10 upgrade isn’t showing up, either your PC isn’t fully updated or your in a waiting list.
In order to upgrade form Windows 8.1 or previous to Windows 10, you need the patch that lets you do the upgrade. To get this, go to the Control Panel -> Windows Updates, then download and install all available updates.
If your Windows 8.1 PC is fully patched but the upgrade to Windows 10 isn’t showing up as a download, you may be in a queue 🙁
Although the release date has passed, not all users have had the upgrade made available to them because it’s too much load for Microsoft to handle in the standard update process.