Originally Posted by Nigeyy

I think the previous poster has the best idea -take it to a shop you trust and ask about what it will cost to change the gearing to ~20 inches keeping components as much as possible. I'd also ask for the prices on the options of changing the chainrings and a new crank and compare. Though I can't be 100% positive, I think it's likely that even if you go to the mtb crank or smaller chainrings, your front derailleur should be fine -but will require repositioning and re-tuning (again another nod to take it to your LBS -they'd probably include this in the price).