Yes, you can easily make a client inactive by searching for them in the Client tab, and then selecting "Mark Inactive". You may also make an inactive client active by doing the reverse. Simply go to the Client tab, select "Inactive" and search for your client by name. Once found, simply click "Mark Active".

You can also remove a client entirely from the program by selecting the "x" to the right of their name within the client list. Please note: once a client has been deleted they cannot be reinstated and this will delete all history (contracts, invoices, etc) for that client. You will have to create a new profile for them.