upgrade from 18.04 to 18.10

 sudo apt update
 sudo apt upgrade
 sudo apt dist-upgrade
 sudo apt autoremove

Will not take from 18.04 to 18.10. They will only get you an Ubuntu 18.04 update. I use those commands, to UPDATE my Ubuntu 18.04. Please see site below.

https://wiki.ubuntu.com/Releases

18.10 will End Of Life July 2019. About a month. Is there a reason you need 18.10?

Check site below.

https://help.ubuntu.com/lts/serverguide/installing-upgrading.html

I only upgrade to new releases, by down loading, burning DVD, then install. Many do upgrade releases the way you are trying, I always have some problem. If you upgrade to 18.10, in July 2019, you will need to upgrade to Ubuntu 19.04. 19.04 will be good to January, 2020. 18.04 is good to April 2023.

adom ; Hello -

The release to be is set in /etc/update-manager/release-upgrades file.
What shows from the terminal command:
grep -i ^prompt /etc/update-manager/release-upgrades
Prompt=lts ??
where in your case you want that changed to "nornal" .

-hope this helps-

The message
"Upgrades to the development release are only available from the latest supported release."
indicates that you tried a release upgrade to Ubuntu 19.10 (which is the release currently in development for publication in October). Such upgrade is only possible if you already have Ubuntu 19.04 running. I assume that you did this with the command
sudo do-release-upgrade -d

If you really want to do a release upgrade from 18.04 to 18.10, then you need the settings "prompt=normal" in /etc/update-manager/release-upgrades and have to execute the command
sudo do-release-upgrade
or follow the prompts that you migth get in update-manager.

You have to be aware of the short remaining life time of Ubuntu 18.10. You would have to do another release upgrade to Ubuntu 19.04 within the coming weeks, and later (between October and the end of the year) another upgrade to Ubuntu 19.10.

 how do i enable the settings "prompt=normal" in /etc/update-manager/release-upgrades
or how do i change the settings?

I tried to do it but i have no luck

# Default behavior for the release upgrader.

[DEFAULT]
# Default prompting behavior, valid options:
#
# never - Never check for, or allow upgrading to, a new release.
# normal - Check to see if a new release is available. If more than one new
# release is found, the release upgrader will attempt to upgrade to
# the supported release that immediately succeeds the
# currently-running release.
# lts - Check to see if a new LTS release is available. The upgrader
# will attempt to upgrade to the first LTS release available after
# the currently-running one. Note that if this option is used and
# the currently-running release is not itself an LTS release the
# upgrader will assume prompt was meant to be normal.
Prompt=lts

adom he; Hello -

A GUI method:
in the software-center -> software & updates -> updates, In the drop down of "Notify me of a new Ubuntu version" choose 'for any new version' .

Else of course is to edit the file with you favorite text editor.

-hope this helps-