Help , Links (Freeware?) etc. for a small Addon Edit

[merry widow]

Hi everyone, I found a theme I really like but I'd like to modify a couple of features if it isn't too difficult. I work extensively with graphics, but have almost no experience with coding (other than the usual CSS, HTML, and a dabble of PHP). How hard is it? And can you recommend tutorials (or even better, an Open Source/Freeware app that helps with it)? Thanks guys.