If you're still keen to try a child theme out, I wrote some training a while back on the subject you might like to have a look at:

https://my.wealthyaffiliate.com/training/adjusting-the-look-of-your-website-with-css-child-themes/what-is-css-and-what-is-a-child-theme

Please let me know if you have any questions!

Mark

Yeah do as Beverley does, feels like a great way to do it :)
Thomas

I use a siterubix site as a test site - so I can always try changes there before doing them on my main site. :) Beverley

Hi - making child themes can be overly complicated.

I would suggest you do as Guy says - just make the changes - you can always change them back if you don't like them. Or download the theme again.

All the best, Mark

Hi, Just take a look here:http://codex.wordpress.org/Child_Themes.
But I think It would not be necessary to create a child theme when you want only to change background color and size.

Don't know about the child theme. Sorry
John

I also don't know how to create a child theme but I would like to learn.

There are many free themes you can use for your site . You should go to wordpress.com and look for a theme that you want to use for your blog .. I'm sure you can find a free theme for that ..