Take it that this is the bike you have, http://www2.giant-bicycles.com/en-gb...llections_id=3 for saving weight, wheels, tires, forks, seatpost, saddle, handlebars in that sort of order, just about everything can be replaced, including the frame but you will find it get expensive very quickly, and if looking for a large weight saving, it can be cheaper to just buy a lighter bike.