Raspberry Pi 3 B+ will not update to 20.04 LTS

I am trying to update my system from 18.04 LTS, but it just won't do it, not from the GUI, not from the command line. When I use the GUI, it says that the update is available, but when I click "upgrade" it crashes instantly. When I use the command line, it shows that about half the packages are not found and it ultimately aborts. I have tried everything which I can find online, to no avail. Thank you for your help.

So it turned out that I needed to first remove a foreign architecture and force part of an older update to install. It then managed to go through with the install and I am now on 20.04.