Use a change management system! Build a test/development system on another server, typically an old retired server. Try not to make major changes to the system during peak usage times of the year. Pick a time when there are very few users on the system. Before changing anything on the production server ensure your backups are working. It is a good idea to keep incremental backups for a period of at least seven days. Upgrading involves three systems: the repository software each year; the server software every three years; and the hardware every four years, if not virtualised or in the cloud. Keep the old machine running for a while until the new machine is stabilised. This way you have a live backup in case of big problems.