apt-get update fail (file not found)

When I try to apt-get update, I have this error:

W: The repository 'http://ppa.launchpad.net/upubuntu-com/flareget-amd64/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
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E: Le téléchargement de quelques fichiers d'index a échoué, ils ont été ignorés, ou les anciens ont été utilisés à la place.

So all you have to do is go to "Software & Updates" tab "Other software" and uncheck or delete the lines for these ppa.