Today I noticed the support for my current Ubuntu version has expired (17.04). To upgrade, I tried apt-get update && apt-get dist-upgrade, but most of the Zesty repositories don't work anymore. (does no longer have a Release file) My update manager and software manager don't give an indication for upgrading at all, refreshing does not work anymore.
Am I stuck with this version or could I still upgrade some way?
archive.ubuntu.com
toold-release.ubuntu.com
(hence 404 errors you didn't mention) which can be dealt with via link already provided. If you're offered an release-upgrade on a non-LTS take it, or stick to LTS versions. – guiverc Jan 25 '18 at 10:12