I upgraded my desktop to Linux Mint 20 Ulyana over the weekend.

Edit your package repository. Replace tricia with ulyana, and bionic with focal.

vim /etc/apt/sources.list.d/official-package-repositories.list

Run update first.

apt update -y
apt upgrade -y

Perform upgrade to Linux Mint 20. When prompted, choose default.

apt dist-upgrade

Reboot.

reboot

cat /etc/os-release.

ulysses@penguin:~/Code$ cat /etc/os-release
NAME="Linux Mint"
VERSION="20 (Ulyana)"
ID=linuxmint
ID_LIKE=ubuntu
PRETTY_NAME="Linux Mint 20"
VERSION_ID="20"
HOME_URL="https://www.linuxmint.com/"
SUPPORT_URL="https://forums.ubuntu.com/"
BUG_REPORT_URL="http://linuxmint-troubleshooting-guide.readthedocs.io/en/latest/"
PRIVACY_POLICY_URL="https://www.linuxmint.com/"
VERSION_CODENAME=ulyana
UBUNTU_CODENAME=focal