I have done as you suggested and created a child theme. I also have installed firebug so I can explore the theme and understand where the changes i want to make are found in the css file but one thing I am confused by. after noting down all the changes i wanted to make I tried it by adding to the child theme stylesheet and it looked all wrong - some changes worked others didn't :-( I think I might have added uneccesary lines in my child theme style.css file.
For example I'd like all the page headings at the top to be in a different colour and lower case. Therefore I have modified them as seen below. Should I be including all the other lines? or just what i have changed (color and text-transform).
thanks for your help - much appreciated
margin: 5px 0 0;