I happen to have a Lumia 520 phone that I was able to upgrade to Windows 10 Mobile Technical Preview a couple of months back. It went smooth and you can following the steps described here to upgrade yours if you haven’t done so.
But I was having trouble upgrading to any newer build releases since then. First of all, I wasn’t aware that I needed to install the Windows Insider app again after upgrading to Windows 10 Mobile. And then, I kept getting this error 0x80240022 telling me that
There were some problems installing updates, but we'll try again later. If you keep seeing this and want to search the web and contact support for information, this may help - (0x80240022)
After patiently trying to get over it many times, I finally gave up and decided that it’s probably a good idea starting from scratch if I want to get on the latest platform. And here are the steps that you can follow.
First of all, download the Windows Device Recovery Tool and install it on my computer. Connect your phone via micro USB, launch the tool and follow the instructions on the screen to reset your phone back to Windows 8.1 platform.
Finish up all updates required for Windows 8.1, then install Windows Insider app from Store app.
Launch Windows Insider app, and follow the instruction on the screen to finish the initial setup. Note that you will need to sign in either a Microsoft Account or a domain account to be able to continue on. Windows 10 Mobile Technical Preview also has 2 update options, Fast ring to get updates as soon as they are available, and Slow ring to get a more stable update. You can pick the update option from Windows Inside App.
Then wait until your phone reboots, go to Settings → Update again, Windows 10 Mobile build should be now waiting there to be installed. The size installation is about 1.5 GB so it may take quite a while to finish.
Once the installation is done, go to Settings → System → About to verify the installation.
Hooray, finally, I am back on track again.