'Located my manual, which is written for models t2326, t2326-04, and t2326-06. For anyone else who has the same question, I've copied the manual's instructions below, along with my appended step, which apparently was omitted for the 06 model.

"Set the ringer

Press PROG. Press the up arrow twice, the name of the current ringer will display and the tone of the ringer will be heard."

[Press the SELECT button (top of PROG button), THEN...]

"Press up arrow or down arrow to scroll through the four ringers. Press SELECT [again] when the desired ringer is displayed and heard.

You'll hear a confirmation tone."

Cheers!