A notebook entry can be deleted as follows:
Open the record associated with the notebook, e.g., the applicant or contact or client
Click View
Click Notebook
Find and highlight the notebook entry to be deleted
Hover on the entry for the Client
Click the "X" to delete it
Click Yes to confirm the deletion
Alternatively, from the list: Open the record associated with the notebook, e.g., the applicant or contact or client
Click Notebook
Find and highlight the entry to be deleted
Click More
Click Delete
If a message appears to tell you that you can't delete it because it is protected, the Protected flag will need to be cleared by the person who created it, which they can do as follows (or a user - most likely a system Admin - with the Permission to unprotect & delete other user's Notebook Items, can delete and unprotect on behalf of any user):
Open the record associated with the notebook, e.g., the applicant or contact
Click View
Click Notebook
Find and highlight the notebook entry to be deleted
Click on the Additional Info tab
Remove the tick from the Protected box
This notebook entry can now be deleted as per the original steps above