first, (assumes you made a Backup of the book someplace SAFE
open the book in the editor: File: Save a Copy (
not in the Library)
(you will add it to the Library later , being CAREFUL to not trip duplicates.
Creat an Empty version eg Book Vol2, drop the book into the details pane)
Now
To delete section, just select them in the Files Browser on the Left: right-click Delete
To Split: View in the Preview pane: Use the folded page (paper air plane like) icon and click when the green line is AT the split point