When you've chosen a template you will see the layout settings for this template below. It consists of a header - with the template name and margins above and below - and a layout screen.
You can change your invoice layout in different ways. The invoice layout always consists of three types of elements:
To change your invoice layout to the format of an American envelope you need to change the source code of your invoice layout.
Go to 'Settings' > 'Corporate style' and select the template for which you want to change the source code. Click 'Source code' and replace the code with the one from this PDF.