I don't really know the free software out there, but I checked your site and don't seen anything complex.
It's looks like plain HTML.
So any HTML editor should do the trick.
Personally I like used Dreamweaver, not free though.
If you need to choose, then I would suggest that you look for tutorials relaying to that product.
Head over to
http://w3schools.com/ to get and introduction to HTML.
For a small fee I can tutor you the first few times