List of devices that are eligible for the update :


What about other devices that are not on this list?


How to download the update (it's not on Settings > Phone Update) :


Feature deprecation
When you install the Windows 10 upgrade, some features currently on your device will be modified or removed, including the following:
* Notifications for missed calls, messages, and emails on contact tiles is not supported.
* Me Tile and Me Card are no longer supported.
* Cortana can no longer search for apps, setting, email, text messaging, contacts
* QR Codes on the device and can no longer open apps through voice commands.
* "Hey Cortana" is no longer available on some upgraded devices.
* Group tiles can no longer be used to receive social networking status updates
* Indoor Maps are no longer available for some locations
* Certain enterprise features, including Data Protection Under Lock, are not available
* Outlook Mail app cannot open .EML attachments.
* Outlook Calendar app does not support Tasks.
* MDM capability to prevent saving and sharing Office documents not supported.

References :

Apparently available from the US store only for the moment. I had no trouble setting region and language to English/US, so it shouldn't be a serious issue (you'd need that to activate Cortana anyway).