You can't change any templates after you've saved them. They're saved as images, so the text or added images don't remain changeable objects once the template is saved.
All you can change for now, is the text box settings.
we should be able to allow certain users to edit our templates (for multi-person announcement templates like this one).
we should also be able to see who made what edits.
oh, and we should be able to make it so that certain users can't edit certain aspects of a template, like fonts and text box locations.