What is best practice for managing templates that require updating monthly?

We have project plans that we use to manage implementations. We're constantly improving them based on user experience or even a new feature being added. We then need to update project plans but when updating a template we seem to have to open the template as a new file, make the change and then save the new file as a template and delete the older one. Is there a way to update templates without having to make multiple iterations of the same sheet?