I cannot update from 19.04 to 19.10 - 'no longer has a release file'

I was attempting to upgrade to the latest LTS but, am required to update from 19.04 to 19.10 first. I have apparently missed the window to do so as when I attempt to do so with sudo apt-get update I get this result:

Ign:1 http://mirrors.digitalocean.com/ubuntu disco InRelease
Ign:2 http://mirrors.digitalocean.com/ubuntu disco-updates InRelease
Ign:3 http://mirrors.digitalocean.com/ubuntu disco-backports InRelease
Hit:4 http://apt.postgresql.org/pub/repos/apt disco-pgdg InRelease
Err:5 http://mirrors.digitalocean.com/ubuntu disco Release
  404  Not Found [IP: 104.24.116.209 80]
Err:6 http://mirrors.digitalocean.com/ubuntu disco-updates Release
  404  Not Found [IP: 104.24.116.209 80]
Err:7 http://mirrors.digitalocean.com/ubuntu disco-backports Release
  404  Not Found [IP: 104.24.116.209 80]
Ign:8 http://security.ubuntu.com/ubuntu disco-security InRelease
Hit:9 http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease
Err:10 http://security.ubuntu.com/ubuntu disco-security Release
  404  Not Found [IP: 91.189.91.38 80]
Hit:11 http://ppa.launchpad.net/ondrej/nginx/ubuntu disco InRelease
Hit:12 http://nginx.org/packages/ubuntu xenial InRelease
Hit:13 http://ppa.launchpad.net/ondrej/php/ubuntu disco InRelease
Reading package lists... Done
E: The repository 'http://mirrors.digitalocean.com/ubuntu disco 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 disco-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 disco-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.
E: The repository 'http://security.ubuntu.com/ubuntu disco-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.

How can I update my existing release so that I can upgrade to a more current LTS? Thank you!