I am running Ubuntu 18.04. I can't update in the terminal. Every time I try (by typing
sudo apt-get update), I get the message:
E: The repository 'http://ppa.launchpad.net/noobslab/themes/ubuntu bionic Release' does not have 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.