From posts I see on other computer forums there are many, including myself, that have not been offered 2004. You can try a manual update, but I would do a full system drive backup (all partitions) to a separate drive before you attempt the update.  If it fails, in most cases it will restore the PC back to how it was before the update attempt but in a few cases the failed update leaves the hard drive corrupted.  You should be doing full drive (all partition) disc image backups anyway - not for IF its needed but for WHEN its needed.  The free version of Macrium Reflect will do the disc imaging.  Macrium Reflect is the most popular disc imaging app. [URL]  
I have 2 Inspiron SFF desktops. One is 14 months old and the other is 12 months old. Both are fully updated with latest bios and drivers. I check for updates to windows manually every week. The 2004 update is still not available on both PCs. I have checked on Dell web and my model has been tested for the upgrade.  Should I install the 2004 update manually or continue to wait for Microsoft. Thanks David
Inspiron 3470 Windows 10 update 2004