How do you make changes to a Word template?
Open the Microsoft Word Template file (*.dotx)
Edit it.
Save it under another name.
Close Microsoft Word.
Delete the original and rename the new one to replace the original.
Alternatives: How to modify an existing template in Word 2007?
To clarify some earlier responses:
It is not necessary to save under other name, delete original, then rename new version, etc. I was doing this myself for a very long time until I found the link below.
http://windowssecrets.com/forums/showthread.php/139163-Editing-a-template-in-Word-2010
As the link and also one of the earlier responses (Deane) said, if you right click on the template icon, click Open, make your changes, and then click Save, you will permanently modify the template in one simple step.
If you just double click the template icon to open it, however, you are not editing the template; instead, you are creating a new document based on the template. This does seem to be "one of those things" in Word. We normally assume that double-clicking to open and right-clicking and then clicking on Open cause the same outcome. Not in this case, however.
When you see a *.doc* document in windows explorer the default context menu option (rght-click) is Open - so double-clicking on the document will open it
When you see a *.dot* document in windows explorer the default context menu option (rght-click) is New - so double-clicking on the document will open a new document based on this template. To edit the template you will need to right click on the document and selected Open from the context menu.