Editing a unit
Editing a book unit
If you want to edit book unit content, then you edit the book from the books listing, not the unit listing. You would then republish the book after which you will see Update to latest version in the unit listing.
If you have added new content then you can also remap the unit to the book as described on the adding a unit page.
Editing a project unit
Editing a project unit is always done from the unit listing. Select the unit to open in the IDE.
If there is a later version of the unit that has been published, you will see the following screen and elect to open either the latest published version or the last version you edited.