Do you mean how do you upgrade a project or how do you upgrade the version?
To upgrade a project, just open it in the new version. Create a backup first. I always recommend creating the backup as a zip file. That prevents you opening it accidentally and working on it before you realise it was the backup. This way you always have a clean backup that can be used to create a new clean copy time after time. I'm not expecting you will have a problem but better safe than sorry.
To upgrade the version, either purchase at the upgrade price from Adobe or your regular supplier. Consider subscription pricing if you upgrade regularly.
See www.grainge.org for RoboHelp and Authoring information