UPDATE / before you start
Step 1: Check Your Current Kernel Version. At a terminal window, type: uname –sr. ...
Step 2: Update the Repositories. At a terminal, type: sudo apt-get update. ...
Step 3: Run the upgrade. While still in the terminal, type: sudo apt-get dist-upgrade.
sudo apt-get update
Hit:1 http://archive.canonical.com/ubuntu focal InRelease
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease
Ign:3 http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu focal InRelease
Get:4 http://security.ubuntu.com/ubuntu
focal-security InRelease [107 kB]
Hit:5 http://dl.google.com/linux/chrome/deb
stable InRelease
Get:6 http://archive.ubuntu.com/ubuntu
focal-updates InRelease [111 kB]
Hit:7 http://ppa.launchpad.net/rvm/smplayer/ubuntu
focal InRelease
Ign:8 http://ppa.launchpad.net/xorg-edgers/ppa/ubuntu
focal InRelease
Get:9 http://archive.ubuntu.com/ubuntu
focal-backports InRelease [98,3 kB]
Err:10 http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu
focal Release
404 Not Found [IP: 91.189.95.83 80]
Err:11 http://ppa.launchpad.net/xorg-edgers/ppa/ubuntu focal Release
404 Not Found [IP: 91.189.95.83 80]
Get:12 http://archive.ubuntu.com/ubuntu focal-security InRelease [107 kB]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/oguzhaninan/stacer/ubuntu
focal 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.
E: The repository 'http://ppa.launchpad.net/xorg-edgers/ppa/ubuntu
focal 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.