The new update for Windows 10 was released for Lumia 550 without a lot of fuss. The update is faced with the firmware version of the handset to 15461.48007 15503.21007 while the version of the operating system remains the same.
It is worth noting that to get this update, you will need a Windows Device Recovery Tool. Note that using this tool, you will lose all your data.
No official information, what exactly does the update, despite the fact that is now available through recovery tool, so surely we are near full package details.