I finally got around to changing out my Christmas blog background...sorry for the lateness (typical). I can never remember how to go about doing this, and I get caught up in the miasma of 'Template Designer'. I am posting this here so that I can remember how to do it next time, instead of having to search for it online or on my computer. I finally figured out that it was simply a "Page Element" matter, where I delete the old code, which is one of the HTML/Java Script gadgets on the right side of the Page Elements Navbar (Note to self: 2nd one from the top), and copy the new code and save. Voila! I have learned a lot from the Background Fairy (http://www.backgroundfairy.com/), and she just directed me to Picnik - the absolute easiest way to add text to a .jpg image for use as a blog header. Of course, being the Johnny-come-lately that I am, I learned that Picnik is closing as of April 12, 2012, but all of their photo editing capabilities will be moved to Google+ (http://www.google.com/intl/en/+/learnmore/). As for now (until April 12), ALL of Picnik's premium content, for which you used to have to pay, is available for free. Go and check it out here.
After uploading your new background and header, go to Template Designer, and choose 'Advanced', to change the colors of the different text elements on your blog to compliment the new background. I have a widescreen monitor, and had black bands on each side of my background, so I changed them to a rosy pink under 'Page Background Color'.