:~$ sudo do-release-upgrade -d
Checking for a new Ubuntu release
Err Upgrade tool signature                                                     
  404  Not Found [IP: 91.189.91.15 80]                                         
Err Upgrade tool                                                               
  404  Not Found [IP: 91.189.91.15 80]                                         
Fetched 0 B in 0s (0 B/s)                                                      
WARNING:root:file 'utopic.tar.gz.gpg' missing
Failed to fetch
Fetching the upgrade failed. There may be a network problem.