To remove a client, pull the client up on the Personal tab, make sure the client does not have any "real" loans (you can check this by going to the Current Loans tab and using the History drop down.
Then click in the Account Number field (the next to last field in the rectangular grid of fields at the top of the Client window). The field will turn white.
Then hold down the CONTROL or CTRL key and type the letter R to remove the client account. The program will ask you to verify the deletion of the account. Answering Yes will delete all client information and all loans and transactions for the client.