Gfilui

Whenever I use sudo apt-get update, this error is shown:

Hit http://ppa.launchpad.net trusty/main amd64 Packages 
Hit http://ppa.launchpad.net trusty/main i386 Packages 
Hit http://ppa.launchpad.net trusty/main Translation-en 
Hit http://ppa.launchpad.net trusty Release.gpg 
Ign http://ppa.launchpad.net trusty Release 
Ign http://ppa.launchpad.net trusty Release
Hit http://ppa.launchpad.net trusty Release
Hit http://ppa.launchpad.net trusty Release 
Ign http://ppa.launchpad.net trusty/main amd64 Packages/DiffIndex 
Ign http://ppa.launchpad.net trusty/main i386 Packages/DiffIndex 
Hit http://ppa.launchpad.net trusty/main amd64 Packages 
Hit http://ppa.launchpad.net trusty/main i386 Packages 
Hit http://ppa.launchpad.net trusty/main amd64 Packages 
Hit http://ppa.launchpad.net trusty/main i386 Packages 
Err http://ppa.launchpad.net trusty/main Sources 
 403 Forbidden
Ign http://ppa.launchpad.net trusty/main Translation-en_US
Ign http://ppa.launchpad.net trusty/main Translation-en
Err http://ppa.launchpad.net trusty/main Sources
 403 Forbidden
Err http://ppa.launchpad.net trusty/main amd64 Packages
 403 Forbidden
Err http://ppa.launchpad.net trusty/main i386 Packages
 403 Forbidden
Ign http://ppa.launchpad.net trusty/main Translation-en_US
Ign http://ppa.launchpad.net trusty/main Translation-en
Ign http://ppa.launchpad.net trusty/main Translation-en_US
Ign http://ppa.launchpad.net trusty/main Translation-en
Ign http://ppa.launchpad.net trusty/main Translation-en_US
Ign http://ppa.launchpad.net trusty/main Translation-en
Err http://ppa.launchpad.net trusty/main amd64 Packages
 403 Forbidden
Err http://ppa.launchpad.net trusty/main i386 Packages
 403 Forbidden
W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-trusty/ubuntu/dists/trusty/main/source/Sources 403 Forbidden

W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-xenial/ubuntu/dists/trusty/main/source/Sources 403 Forbidden

W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-xenial/ubuntu/dists/trusty/main/binary-amd64/Packages 403 Forbidden

W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-xenial/ubuntu/dists/trusty/main/binary-i386/Packages 403 Forbidden

W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-trusty/ubuntu/dists/trusty/main/binary-amd64/Packages 403 Forbidden

W: Failed to fetch http://ppa.launchpad.net/beineri/opt-qt57-trusty/ubuntu/dists/trusty/main/binary-i386/Packages 403 Forbidden

E: Some index files failed to download. They have been ignored, or old ones used instead.

==============================================================================This is my sources.list

# deb cdrom:[Ubuntu 14.04.4 LTS _Trusty Tahr_ - Release amd64 (20160217.1)]/ trusty main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ trusty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse

deb http://us.archive.ubuntu.com/ubuntu/ trusty-security main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-security main restricted
deb http://us.archive.ubuntu.com/ubuntu/ trusty-security universe
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-security universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-security multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu trusty partner
# deb-src http://archive.canonical.com/ubuntu trusty partner

## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu trusty main
deb-src http://extras.ubuntu.com/ubuntu trusty main
deb http://us.archive.ubuntu.com/ubuntu/ trusty-proposed main universe multiverse restricted


## Update for Codeblock by Chunting
# deb http://apt.tt-solutions.com/ubuntu/
# deb http://apt.tt-solutions.com/ubuntu/

How could I fix it? Since I'd like to upgrade my OS from Ubunt 14.04 to 16.04

I think the solution is simple - disable non-existing repositories (opt-qt57-xenial and opt-qt57-trusty):

sudo add-apt-repository -r ppa:beineri/opt-qt57-xenial
sudo add-apt-repository -r ppa:beineri/opt-qt57-trusty

sudo apt-get update

Then add existing Qt 5.7.1 PPA if you need this version:

sudo add-apt-repository ppa:beineri/opt-qt571-trusty
sudo apt-get update
sudo apt-get dist-upgrade