Hello!
Below is how you install Deluxe and Premium Deluxe after the Standard version has been downloaded:
Go to menu / Profile / Content manager / and selected “toggle all” now the button says “Download Selected” so that you can install the additional goodness of Deluxe (?GB) and Premium Deluxe (3,79GB). 
Note, that you might have to enter, wait a bit and re-enter a couple of times into the Content Manager and packages will show up eventually. This has been the case for a MS Store purchase. For Steam purchase the packages might be available later but as soon as possible.
Before:
After:
Cheers, Scuby
8 Likes
Sorry, but I do not get the download now choice. And I have the receipt from MS for $127. I want my stuff!
Same here … not getting it
Ditto. Been trying for 2 days now.
Ahh Entitlement Management. (A fancy way of saying what a user is allowed to download)I remember doing this at a previous Game’s Industry job.
It is always a chore to get it working right! 
I bought MFS Premium Delux and just downloaded this package. Do I need to download anything else?
The solution to this problem for me was in my ESET permissions for FS2020. I had to enable “both” in directions and boom it worked.
I just put a new m.2 in and thus had to reinstall. This is the solution that worked for me.
Take care and all the best!
I tried Scuby’s method. A couple of airports were ready for updating but no sign of the 5 extra aircraft that I paid for (p. Deluxe) and never did get.
