Just be honest and get it done. Tell them that you expect better performance from a designer that works for you. Then let them go. Consult with HR/lawyers as ne

Just be honest and get it done. Tell them that you expect better performance from a designer that works for you. Then let them go. Consult with HR/lawyers as needed. Whether someone is close but not quite at the bar, or far from the bar, your conversation is pretty similar.