I'm new to WordPress and am about to make my first website. I've watched a bunch of tutorials on how to use it and have experimented with making a website based on the "Twenty Ten" theme.
My question is:
Am I allowed to take one of the existing free themes that are available on WordPress and make changes to it? For example: I like the "Elegant Grunge" theme by Michael Tyson but the header is all black with no option to change it. Can I activate that theme, and then try and find the php file that controls the header and modify it to allow me to have a picture as my header? Am I breaking some law or WordPress code of conduct if I do that or make other changes of that nature?
My apologies if this is a really basic question. I just want to make sure I'm doing things properly and not stepping on toes.