It's depend, buddy. If you have no clue about PHP and HTML, then don't touch the code or you'll break the theme.
I think yes. You can edit the code of a free wordpress theme as far as you maintain footer links (sponsored,theme designer links etc.) intact there. DON.
Thanks for the info guys. I did change some parts of my wordpress blog and was afraid that I might get in trouble when doing such editing.
As long as you dont call it your own, still give credit to the designer/sponsors, but yeah editing is fine.