We just gave you the good news, now here’s the caveat. In order to work around a bug that black screens your phone after installing Windows 10 Mobile 10549 from a previous W10M build, Windows Insiders must update from Windows Phone 8.1:
We discovered a bug late last night that caused phones upgrading from Build 10536 to get stuck at a black screen after this new build is installed. Rather than making you wait a little bit longer for us to fix this bug – we decided to release this build as a single update from Windows Phone 8.1.
Microsoft hinted at one possible reason for having users start from 8.1, “We know having to go back to Windows Phone 8.1 to get this new build is a bit of work. By doing so you are also helping us test the upgrade path that millions of Windows Phone 8.1 customers will take to upgrade to Windows 10 Mobile, so we appreciate the adventurous Insiders who choose to go this route and give us feedback”, so at least there’s some good that will come of this.
So if you’re currently on a previous Windows 10 Mobile build and want the latest bits, you’ll need to use the Windows Device Recovery Tool to go back and re-install Windows 8.1, then install the Windows Insider app, and then you should be able to install the latest bits. If you’re not seeing the latest updates from your Windows 10 Mobile device, that’s why.
Further reading: build 10549, Windows 10 Mobile