My brother also uses Duolingo and his interface shows lessons as circles with radial progress segments, whereas mine shows rectangles with a progress bar at the bottom. Any help on how to move to the newer circles (they look a lot nicer)?
Your brother has the newer version of the Duolingo interface, which hasn't been released for everyone yet -- only to newer signups.
There's a bit more explanation here:
My husband also has the interface like you describe, while I have the newer one. It's been interesting to compare!