Microsoft will begin the roll out of Windows 10 for phones in December. Existing Windows Phone devices will begin receiving the software in a couple months, but it could take another few months for everyone to gain access to Windows 10 Mobile. Since Windows 10 Mobile requires 8 GB of storage, some phones won’t be receiving it.
If you want to avoid waiting for your carrier to deliver the update, you can become part of the Insider Program.
Microsoft is reportedly close to delivering the Windows 10 Mobile RTM and it is only dealing with a few bugs at this point.