To save storage space, you can remove all your books from your eReader. Any Kobo books you remove from your eReader will still be available on the Kobo Cloud. 

1. Go to your Home screen.
2. Tap My Books at the bottom of the screen.
   
   
   
3. Tap the  Menu icon.
   
   
   
4. Tap Manage downloads.
5. Beside Downloaded Kobo Books, tap Remove all. 
   A dialog window will appear.
6. Tap Remove.
7. Any downloaded books on your eReader will be removed.