Note that you usually don't have to open the Normal template to change the
Normal style. In a blank document (create one by pressing Ctrl+N), click
Format | Styles and Formatting. In the task pane, right-click the Normal
style and choose Modify. Click Format, Style and change the line spacing as
desired. Click OK. Make any other desired changes. Click "Add to template,"
and then click OK. If/when you are prompted to save the Normal template,
choose to do so.