This lesson will very quickly go over the basics of changing a field on a default template.
Open up the document template you wish to edit in Word.
Right-click on the field you want to edit and click edit field.
Its important that you don't just edit the name here, as this will not work.
Type or copy and paste the new field you wish to use.
A full list of available fields is here: http://support.servicem8.com/entries/388498-what-fields-are-available-for-the-invoice-quote-work-order-templates
At this point you may need to correct your font type and size.
Repeat for any other fields you wish to change.
If it helps design, you can actually shorten this text without effecting the merge field. Ensure it doesn't have the spell check red line underneith though as this will break the link.