This dialog box also allows to remove user-defined document templates. In order to do this, simply click on a template in the "Existing document templates" list and then click on the button.
Note that this operation takes immediate effect: clicking on the Save Document As Template" dialog box will not cancel the deletion of the template[21].
button of the "You can only remove the document templates you have created. You cannot remove predefined (grayed) document templates.
In the above screen shot, notice how removing user-defined template called "Refentry" would restore the predefined template having the same name.
[21] The button of the "Save Document As Template" dialog box just cancels the action of creating a new template.