Once you have downloaded your template and unzipped it. You will need an HTML editor. Here are a few of your software choices.
CoffeeCup HTML Editor - (Free trial) Edits HTML 4.01 and HTML5
For editing any Allwebco template. Works with HTML 4.01 and HTML5. Available for PC or Mac OSX. A free light version is available with the full version available as a 30 day trial. See the CoffeeCup website
Nvu (Mozilla) - (Free) Edits HTML 4.01 and HTML5
For editing any Allwebco template. Even though it is older software it works well with both HTML 4.01 and HTML5. Available for PC or Mac. Built on the Netscape editor platform. See Nvu website
Notes: Will show a "can not edit page" message for HTML pages with iFrame code, however the error is for the "framed" page and will not affect editing of the main page.