The front chainring is attached to the crank arm so you'll have to replace the whole crankset to use a larger chainring (would be a nice upgrade to do, anyway). I just got a Nova, as well, and am doing the opposite...stripping of the gear cluster and making it a single-speed. Putting a 16T freewheel in the rear almost worked without a chain tensioner so I'm going to try a 17t before I resort to a tensioning device. It would be nice to find a "magic gear" combination, so I could try a fixed hub later, if I want. Otherwise, the only option is to buy a $$$ eccentric hub.

Good luck.