I did not know that the F6 was still made in 2013, but for the 2012 model, the 6 had the same frame as the 5, 4, and I am fairly sure the 3. The 2 had its own frame, and the 1 had its own frame. So it is the components and wheels that made it the lowest entry, and not the frame.
If you like it, it fits, and it isn't broken, keep it and ride it. If you hanker to upgrade, do wheels first, as they are portable even if you decide on a different bike. For $600 or less (in some cases much less), you can get a quality aluminum rimmed wheel with nice hubs which should feel like an improvement over stock.