edit
/etc/apt/sources.list
with following
## EOL upgrade sources.list
# Required
deb http://old-releases.ubuntu.com/ubuntu/ CODENAME main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-updates main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-security main restricted universe multiverse
# Optional
#deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-backports main restricted universe multiverse
Replace CODENAME
with your distribution codename
you can get it with
lsb_release -a