I am finding it tedious going through repeated material that I know. How do I change the level to be more challenging?
Congratulations on completing your French skill tree!
You will learn much more French words and more difficult sentences by using the "Strengthen" features.
Here is the link to "Best Way to Make Your Tree Turn Gold and Stay Gold"
Other ways you could improve your French:
The reverse tree, the course English for French speakers, is very useful. There you have to translate much more from English to French.
Here is the link to the Duolingo Help Center for
"How do I switch my Duolingo course language?"
Use the web version of Duolingo (http://www.duolingo.com) instead of the App. The web version works also in the browser of a tablet or Android phone.
Try to read and write in Duolingo's French discussion forums. There you will find the daily used words, sentences and idiom.
Apart from that
- read a newspaper article every day and try to learn its new words
- listen to podcasts, watch movies with or without subtitles
- converse with a native speaker as much as possible
- write smaller texts, upload them on http://translatihan.com/ and let them be corrected by native speakers a.s.o.
There are numerous possibilities. Duolingo will only bring you to an A2/(B1) skill level in reading/writing and A1 (maybe A2) in listening/talking.
Info about language levels:
Read from "Common reference levels".
Some people suggest doing the reverse tree in Duolingo, "learning" your mother language from your foreign language (English from French), although you can turn off the pronunciation exercises in your settings. This allows you to learn some different expressions, from another perspective.