I have the same issue - trying to update from 1709 to 1803 getting error Error 0xc1900204 - trouble with the manual update you suggested there is you don't get the option to keep all your files, etc. so everything gets wiped.
Auld-Yin - there's some drivel being posted here - Mr Bane is giving you the correct advice whichever version of
windows you're using. Go to updates in control panel & select each update in turn and do them one at a time.
Windows often screw up and one update conflicts with another and until they realise and issue a fresh update
you see these errors. If it throws up an error code at any stage Google that and on the microsoft website they
usually give a solution.
I'd add to that cars, gas boilers, toilet cisterns, lawnmowers. I even got asked once if I knew anything about radial engines. Some folks seem to think that if you know anything about IT, you can fix everything.
For many, the Windows 7 update became so slow it was unusable. All night updates, or even longer, were common. There were two fixes (KB3020369 and KB3172605), which needed to be downloaded and then applied in that sequence in order to sort the problem.