If all you want is to be respectful and professional just call or email your T, thank them for what they've done so far and tell them politely that you feel that you need something different at the moment and, therefore, you'd like to end your work with them.

If you feel you have a good connection with your T and would like to say good bye properly, then do it in person.

Other than that, there is no right or wrong way for you to terminate therapy. Do whatever you are most comfortable with. You, as a patient, have no obligation to terminate therapy in any particular way.