Make a Child Theme: The first thing to do is to make a child theme. This is pretty easy, so research it. You really need only two files: style.css and functions.php. If the theme writer ever updates the theme for security or other reasons your changes will not be wiped out but overlayed on top of the update.
Style.css: I added a dropcap, indented paragraph and lists. The dropcap is a tip pf the hat to typesetting, pretty much lost in this day of internet. The indented paragraph I simply could not do without. Indented paragraphs simply make reading text easier. The original theme did not allow for bulleted lists. You could code a list but the bullets would not appear. I redefined the css for lists, but this added bullets into the sidebar. I’ll look into fixing this later.
Header.php: The new version of the theme came with a different graphic, one of fire, red, orange in colour. I wanted to stick with the original macro screw in cold metal grey. The new theme could not find my graphic, so I had to change the URL in the code.
Functions.php: I wanted to slim down the Meta widget section, so took some code to redefine the core’s default-widget.php. The code cancels out the default function and then reassigns it to my new function. This code to mod the meta links worked really well. I did check it against version 3.6.1 and it is identical. Because I would rather have the indents I took the code from the WP source and then changed it.
Sidebar.php: The Bookmark I never used, so I pared it down. The site links were old anyway. Old stuff is not necessarily worse and new stuff is not necessarily better.