How to update a project

Further to a thread on my old projects producing backup files called “Filename.backup.scriv” in the old manner, I’m told that updating the projects would stop this behaviour.
How do I update a project, please?

You open it eith a newer version of Scrivener.
Old Scrivener 2 projects can be opened by Scrivener 3, and will then be saved in the new format. The old version will also be saved but with a name telling you it’s a backup in the old format.