From within a library: library settings are accessed from within the library by clicking the cog icon on the toolbar.
From the teacher dashboard: library settings are accessed by clicking the three dot menu of the library card.
When the settings page is displayed you'll see the name of the library at the top of the page, click in the field to edit the name of the library. Changes are autosaved.
To discover more ways to configure your library and student permissions visit the Library settings support article.