I am on a Chromebook and am running a chroot. My Ubuntu version is 16.04.6 I want to upgrade to a newer version. Is this possible? If I look online, it says to open a program called update manager. For me, that program does not exist and when I type in the command to get that program, it says HTTP quit unexpectedly. Can anyone help?
Is there a program called "Terminal"? Open that and type sudo apt. There will be shown a list of most used commands or at least a list of commands. You are looking for the dist-upgrade command or the "sudo do-release-upgrade" command.
Check if The standard Ubuntu Software application can be run and go to the updates section. You can select many software sources here. Select all sources and newer versions and apply. Then try updating again. If you cant even update an upgrade is unlikely too. Try this first.
This might be of help https://www.cyberciti.biz/faq/how-to-upgrade-ubuntu-16-04-to-18-04-lts-using-terminal/