www.belightsoft.com/disccover Start of Help > Document Layout > Custom Templates for Papers and Trays

Customizing a Pre-Defined Template

To modify a pre-defined template, select it in the list and click the Customize button.
Then follow the steps described in Creating a Custom Template.

Note that if your goal is changing the label dimensions (not changing its location on paper, or adding/ removing labels), you can set new size on the Design Element tab in the Inspector.

By customizing a pre-defined template, you cannot overwrite it, but save its modified copy as a custom template.