You can delete a duplicate client entries by selecting the client and then using the x at the top ribbon to delete the entry as shown below:
You will be given a warning prompt to confirm that you really want to delete the client entry. Deleted entries cannot be brought back to the system and by deleting the client, you also delete all of their holdings and goals information as well (as well as all the reporting).
To delete any holding or goal information, navigate to the correct area and delete the entry by selecting the x symbol as illustrated below: