Want advice to remove line from Twenty Ten theme

I am a novice. I am building a site using the Twenty Ten theme. At the bottom of each page I create, there is a single text line containing the site title on the left side and on the right side the words “proudly powered by WordPress”.
I would like to remove this line, or change the contents. Is that possible? It does not appear to be a footer widget. I have tried adding a footer widget hoping to replace the line, but the line remains. I apologise that I am unable to provide a link to the site as it is down at the moment!!