I'm also having an issue with a download.  Was able to get the upgrade for a client's version, but do not think have the upgrade on my own despite being told my version (Sage 50 Accountant) is up-to-date.  I have Release 2020.2.  Am I up-to-date?  Will need to migrate data between my computer and my client's tomorrow.

Yes 2020.2 is up to date.  You should have the file automatically downloaded to 

C:\Users\Public\Documents\Sage Software\Simply Accounting\Download

Assuming your settings are set to download automatically.

You can check this by going to Help, About Sage 50..., Support Info, Modify Product Update Settings.

I turn off the Automatically Install Product Updates but have the Automatically Download option turned on.

The Knowledgebase article #98686 may be able to help you.