While using older images of raspberry pi, the upgrade fails with the repository 404 not found.
The reason is the older images repository is moved to legacy.raspbian.org.
I ran into this same issue but didn’t want to go through the work of upgrading versions,
so simply updated the mirror link in my sources.list from mirrordirector.raspbian.org to
legacy.raspbian.org
sources.list
deb http://legacy.raspbian.org/raspbian/ jessie main contrib non-free rpi
# Uncomment line below then ‘apt-get update’ to enable ‘apt-get source’
#deb-src http://archive.raspbian.org/raspbian/ jessie main contrib non-free
Source: linux – Debian apt-get update 404 not found error – Super User