To deactivate a client, click on your Admin button --> in the dropdown menu click Clients --> go to the desired client --> scroll down to the Status section and click "Deactivate."
The Status will now read "Inactive":
At any point, click on the "Activate" button to reactive the client.
You'll also be able to tell if a client is inactive because the name will read "[Client Name] - INACTIVE":
You'll still be able to search for inactive clients on the Clients page. You can tell if a client is inactive here, too, because they'll appear as grey (versus active companies who show in white columns):