I am currently using 19.04 and I got "No new release found for 19.10"

Upgrades from previous versions are only switched on by the release team when they are are happy that there are no massive upgrade bugs hiding anywhere.

In the past, this has varied from enabling them later on the actual release day, all the way to nearly a week after release. There is absolutely no fixed rule.

In the case of this release, when I queried with Adam Conrad (Ubuntu Release Team) on IRC on Friday 18th October, I was told that they were vaguely undecided on whether to 'just do it' that day or 'maybe wait for a weekend of potential bugs to roll in and re-evaluate on Monday'. Obviously the latter won out.

As have been explained you can force the upgrade by appending '-d' when manually running the release upgrade tools. This has the effect of making the release upgrader check against this development release meta file where Eoan is still the development release and upgradable to, instead of the proper stable release meta file where it has not been added yet. If you do so before before the release team decide to pull the trigger, you are basically becoming an at your own risk tester of this process.

Rik Mills.

K/Ubuntu Developer

It will appear one week after the release. Until then it still is considered a "development" release. You can get it anyways when specifying -d:

do-release-upgrade -d

Source: Ubuntu Tutorial

Looks like you need to wait a few days, or force the update with the -d flag

For me, also, sudo do-release-upgrade -c reported no new release.

So, next I tried upgrading 19.04 to 19.10 using
sudo do-release-upgrade -d (instead of -c)

The good news is this resulted in an upgrade to 19.10 after a couple of hours with brief pauses for permission to use distribution versions of a couple of files instead of my customized versions. However, the bad news is that I had no GUI login prompt after the upgrade. I could SSH in remotely but could not login locally. I tried fixing the problem manually and it didn't help.

Next, I tried this again on another computer. The end result was the same as the fate of the first computer.

After that, I restored the two computers from the backups I made just before attempting the upgrades. Both computers are back on 19.04 and are working properly. I will try again in a few weeks.

I found a solution and want to share it.

The issue was that I had no GUI login prompt after the upgrade from Ubuntu 19.04 to 19.10.

The actual problem turned out to be that the GUI login prompt doesn't appear if Wayland is enabled on Ubuntu 19.10 and Ubuntu is running on Virtual Box on Windows 10 just.

My solution was to get into Ubuntu desktop by ssh, then edit /etc/gdm3/custom.conf, uncomment WaylandEnable=false in the [daemon] section, and reboot. And with that, I got the GUI login prompt and was able to login and enjoy Ubuntu 19.10.