Ubuntu Linux 18.04 LTS standard support ends today (31/May/2023) unless you get Expanded Security Maintenance (ESM). Here is how to upgrade from Ubuntu v18.04 to 20.04 LTS https://www.cyberciti.biz/faq/upgrade-ubuntu-18-04-to-20-04-lts-using-command-line/ or Ubuntu 20.04 LTS to 22.04 LTS https://www.cyberciti.biz/faq/upgrade-ubuntu-20-04-lts-to-22-04-lts/