david@Ubuntu:~$ sudo apt update
[sudo] password di david: 
Trovato:1 http://it.archive.ubuntu.com/ubuntu xenial InRelease
Ign:2 http://ppa.launchpad.net/relan/exfat/ubuntu xenial InRelease             
Trovato:3 http://it.archive.ubuntu.com/ubuntu xenial-updates InRelease         
Trovato:4 http://security.ubuntu.com/ubuntu xenial-security InRelease          
Trovato:5 http://it.archive.ubuntu.com/ubuntu xenial-backports InRelease       
Err:6 http://ppa.launchpad.net/relan/exfat/ubuntu xenial Release              
  404  Not Found
Lettura elenco dei pacchetti... Fatto                
E: The repository 'http://ppa.launchpad.net/relan/exfat/ubuntu xenial 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.
david@Ubuntu:~$