When a page has been edited, it can either be updated immediately by clicking the 'Update webpage' button, or it can be saved as a version for uploading at a later date.
To access previously saved versions on a page, click 'Edit webpage', then click on the 'Load version' tab. You will then see a list of saved versions with the most recent version at the top.
If the status of a version has 'published' next to it, this means that it would have been live on the site at some point, however, if it says 'Saved', this means that the page was only saved and never published.
Loading a version takes you to the page editor where you can edit the version before either saving it as a new version, or updating the live site.