To customize the invoice print layout, open the invoice and press View Invoice
Next click on the Customize button on the tool bar
In the opened questions press Yes
Next MS Excel will open with the invoice template, as bellow:
You can customize the template by changing fonts, color and styling. Save and exit MS Excel when you're done.
You will be able to use the new template each time you View Invoice:
The custom template names can be renamed from Administration -> Report Templates. Right click on the template to rename, select Rename and enter the the new name.