To change the preview of the Quotes, Proforma and Order of a sale ,you must be Administrator.
You will find those 3 options in the preview of a sale :
Click on preview :
In this example, the preview is on the quote with Photo material Quote as a model.
To modify "type" details, go to the Administration module.
Then left menu, Documents and Documents Settings.
On the right, you will find a list of items :
Each item corresponds to the preview of your documents.
If, for example, you click on Invoice, you will be able to modify the view of your invoices in detail : Logo, Sales terms, footer, banner, display size, etc.