The reports are styled using Themes in Microsoft Word. You can learn more about themes here:
http://office.microsoft.com/en-us/word-help/CH006354177.aspx
If you'd like to change the style of all the reports you create, your best bet is to create a theme with the look that you want. Then edit the template by just changing which theme it uses (probably a theme you created). That way, you don't need to change the style of each element in each report individually.