Não consigo retornar um comando Update positivo do Terminal,como resolver isso?

ABAIXO TODO O RETORNO DE QUE ACONTECE COM O COMANDO SUDO APT-GET UPDATE!
se puderem ajudar agradeço muito

Atingido:1 http://br.archive.ubuntu.com/ubuntu xenial InRelease
Atingido:2 http://br.archive.ubuntu.com/ubuntu xenial-updates InRelease
Atingido:3 http://br.archive.ubuntu.com/ubuntu xenial-backports InRelease
Obter:4 http://packages.elementary.io/appcenter xenial InRelease [6.129 B]
Atingido:5 http://security.ubuntu.com/ubuntu xenial-security InRelease
Obter:6 http://packages.elementary.io/appcenter xenial/main amd64 DEP-11 Metadata [78,6 kB]
Ign:7 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial InRelease
Atingido:8 http://ppa.launchpad.net/elementary-os/stable/ubuntu xenial InRelease
Atingido:9 http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu xenial InRelease
Atingido:10 http://ppa.launchpad.net/noobslab/apps/ubuntu xenial InRelease
Atingido:11 http://ppa.launchpad.net/noobslab/macbuntu/ubuntu xenial InRelease
Atingido:12 http://ppa.launchpad.net/elementary-os/os-patches/ubuntu xenial InRelease
Atingido:13 http://ppa.launchpad.net/philip.scott/elementary-tweaks/ubuntu xenial InRelease
Ign:14 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial Release
Ign:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Ign:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Ign:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Ign:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Ign:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Err:15 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 Packages
404 Not Found
Ign:16 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main i386 Packages
Ign:17 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main all Packages
Ign:18 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt_BR
Ign:19 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-pt
Ign:20 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main Translation-en
Ign:21 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:22 http://ppa.launchpad.net/elementary-br/projects/ubuntu xenial/main DEP-11 64x64 Icons
Baixados 84,7 kB em 57s (1.463 B/s)
Lendo listas de pacotes... Pronto
W: The repository 'http://ppa.launchpad.net/elementary-br/projects/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.
E: Falhou ao buscar http://ppa.launchpad.net/elementary-br/projects/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Falhou o download de alguns ficheiros de índice. Foram ignorados ou os antigos foram usados em seu lugar.