Before you update Narrative please ensure that Narrative is in your applications folder.
1. Open Narrative
2. Select 'Narrative' on the menubar
3. Select 'check for Updates'
4. If an update is available, select 'update' to start the download and perform the update.
Now you are up to date.
NB. we highly suggest enabling Automatic updates as we frequently keep Narrative updated for bug fixes and feature updates