1. Delete all payments under the Payments tab of the case being deleted.
2. Delete all invoices of the case
3. Delete all time/expense entries.  These entries need to be deleted one by one.
4. Under the Edit Case tab, scroll down to find Delete Case button.

To delete a client, follow points 1-4 above for every case of the client being deleted.  Then click on the Trust Transactions tab of the client.  Delete all trust transactions.  Then under the View Client/Edit tab, click on the Delete Client button.  Refresh screen.