Word has a standard document template called 'Normal.dot'. If you want to change any part of the formatting of this template, you have to delete it and create it again.
Launch Word normally. Set up a document with all of the formatting that you want. Save it as a document template to the folder C:\Users\YOURUSERNAME\AppData\Roaming\Microsoft\Templates(**see my note below)
Make sure you save it under a name that you will recognise, but NOT Normal.dot.
Now close Word. Go to the folder above and rename the file Normal.dot as Normal.old. Then rename your newly created template file as Normal.dot.
Next time to you launch Word your newly formatted template should open by default.
** Note that Microsoft regularly change the location of the template folder in different versions of Windows, just to confuse us. Yours may be in a different location to this.