In the top right corner, where it says "nickb is learning <whatever language you're learning>", click on the language. There should be a drop down list, from which you can select the language you want to learn.
I am currently learning languages in English, e.g - English to Swedish and English to French. I have also started learning French to English. How do I go back to the French to English page, now that I'm in my English portion of Duolingo?