Ubuntu APT repositories not found when updating

I see that you are running Ubuntu 14.10, which reached End of Life status on July 23, 2015 at which point all of the repositories were taken offline. Ubuntu releases twice a year - in April (x.04 releases) and October (x.10 releases). The standard support window for an Ubuntu release is less than 1 year, while the LTS versions ("Long-Term Support", released every 2 years) get a 5 year support window. The LTS versions are pretty much always released in April, so an x.10 release would only ever be supported for a relatively short time. At present, the supported LTS versions are 14.04, 16.04 and the current, 18.04. If you install any of these versions instead, you will get a longer support window. It is worth noting that 14.10 should have less than 1 year of support left at this point, so it's likely not worth installing that one at this point. You can find out more about Ubuntu release cycles on their Releases Page.

If you plan to upgrade to a newer version, it is recommended to create a new server and then copy your data over with a tool like rsync, as it's been my own personal experience that in-line Ubuntu upgrades have a higher than average tendency to be problematic.