How do I update Ubuntu 18.10 to 19.10?

Hi,

I’m running Ubuntu 18.10 in my droplet. But I haven’t updated it in a while. When I tried to run do-release-upgrade I getting “Please install all available updates for your release before upgrading”.

But when I tried to run sudo apt update && sudo apt upgrade -y getting these in the terminal:

Ign:1 http://mirrors.digitalocean.com/ubuntu cosmic InRelease
Hit:2 http://ppa.launchpad.net/certbot/certbot/ubuntu cosmic InRelease
Ign:3 http://mirrors.digitalocean.com/ubuntu cosmic-updates InRelease
Hit:4 https://repos.insights.digitalocean.com/apt/do-agent main InRelease
Ign:5 http://mirrors.digitalocean.com/ubuntu cosmic-backports InRelease
Ign:6 http://security.ubuntu.com/ubuntu cosmic-security InRelease
Err:7 http://mirrors.digitalocean.com/ubuntu cosmic Release
  404  Not Found [IP: 104.24.117.209 80]
Err:8 http://security.ubuntu.com/ubuntu cosmic-security Release
  404  Not Found [IP: 91.189.91.39 80]
Err:9 http://mirrors.digitalocean.com/ubuntu cosmic-updates Release
  404  Not Found [IP: 104.24.117.209 80]
Err:10 http://mirrors.digitalocean.com/ubuntu cosmic-backports Release
  404  Not Found [IP: 104.24.117.209 80]
Reading package lists... Done
E: The repository 'http://mirrors.digitalocean.com/ubuntu cosmic Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://security.ubuntu.com/ubuntu cosmic-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://mirrors.digitalocean.com/ubuntu cosmic-updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://mirrors.digitalocean.com/ubuntu cosmic-backports Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

How do i fix this and upgrade to newer version?

Thanks!