In the last week I've experienced some glitches that I want to mention so you can watch out for this stuff...
Trying to install the 2nd June cumulative update for win10 1809, Windows Update wasn't writing to disk, with RAM usage growing instead -- shut win10 down when RAM use reached 4 GB, and when restarted it worked normally.
If/when you click to check for updates, win10 will tell you either the new version, 1903 is available to download, or tell you that your device isn't ready yet. In the latter case it has a link to learn more, which is useless -- just takes you to the list of problems Microsoft knows about, but not which one is preventing the 1903 upgrade. After installing the 2nd June 1809 cumulative update, Windows Update changed the message from couldn't install to could. I don't know for sure if that was because Windows Update screwed up the 1st time, or if that update fixed a problem, or if they're adding fixes to the 1903 setup that are not listed on their web site. The 2nd option, that a fix was included in the 2nd June update, is *probably* the reason, since it included: "Addresses an issue with evaluating the compatibility status of the Windows ecosystem to help ensure application and device compatibility for all updates to Windows", but since I don't know for sure why it was refused, can't say 100% what the fix was.
I allowed my wife's 2-in-1 to download & install win10 1903 via Windows Update. That worked normally for my son's PC, but on the 2-in-1 I gave up & turned it off when after 4+ hours it had just reached 93% [it was 2:00 AM]. Next morning I had it resume the setup, which started at 25%, but finished in a couple of hours. That's still messed up though -- I copied the setup files from the win10 ISO to the hard drive on the mini PC, which is less powerful than the 2-in-1, and the upgrade took roughly an hour.