To customise any of these templates, click the (+) button adjacent to required template. The steps in the pop-up window here are the same as those when creating a Voice Message in the Record Voice Message Window.
The Placeholder column shows the name given to a library entry. Some are allocated by default during account set-up; e.g. "Organisation" by default plays the name "Groupcall", but you can change this to your school name simply by recording a new name via the + button.