In production, use even number versions like 4 or 6, these are the Long Term Support versions that will be patched for a certain time. These are the versions at which node.js is considered production-ready. The odd number versions are not LTS and you should generally stay away from them if you're worried about production stability.
You should use NVM for managing versions, switching out a version is as easy as a single command, not to mention installing node.js through NVM takes care of every single permissions mumbo-jumbo problem I've ever encountered (global installs, jumbled installs, unhelpful or uncommon errors) and seen people inquire about. After NVM, node stopped being about googling problems and became a smooth experience.
Upgrading node.js should not be very necessary unless your project calls for it (medium to large scale, you have read changelogs and understand some new feature or fix that will benefit you greatly), or you're upgrading to a minor/patch version like from 6.0.0 to 6.2.14 or something (fyi those are not real version numbers). In which case you had better written a comprehensive test suite with 100% coverage so you can make sure things are still functioning after you punch in that aforementioned single NVM command.
If you're later upgrading from 6 to 8 then your tests better have tests ;) /s