Major updates are normally rolled out to the billions of windows machines over the course of a few months. I haven't been keeping up with the news for v.2004 specifically but It wouldn't surprise me if the launch was going exactly to plan and wasn't delayed.
As Iceman says you can force it if you'd like but unless you need a particular feature it adds then I'd just let it do it's own thing.
There are still significant bugs that Microsoft is working on that affect computers with certain chipsets, graphics chips, or particular configurations etc on here is a link to the MS website to explain
View announcements and review known issues and fixes for Windows 10 version 2004 and Windows Server 2004
I updated my desktop and laptop briefly before rolling back due to minor bugs e.g. SSD trim buggy, erroneous pop up “there is no email client configured for this action”, NextPVR not working well”. These are exactly the reasons you shouldn’t upgrade immediately.
If you don't want to go back to the old version then yes this can be deleted.
I would personally do it via the disk clean up till included in Windows though.
Bring up windows explorer navigate to your c drive, which is normally under my computer. Right click on the c drive and bring properties. I think it's in the first tabs (not on my pc at mo) but there is disk clean up option. Click on that and then select system files as well (you will get an admin prompt, select yes) and it will work out what can be deleted and how much space is taken. Check the ones you want and click tidy. It might take a several months depending on how much but should help you
Damn phone autocorrect Should say several minutes depending on whether you have an SSD or HDD etc.
Mine have usually stuck around on some machines (or I was possibly impatient).
It's worth running the tool anyway to see how much space is used up in various areas, especially the system variant. Running the tool does not do anything other than calculate the space, you then have to have to agree to let it remove. It often brings more usage than you think.