PLS HELP!

Guys! Ang lakas sa gas nung optra namin,mga 6km/l lang city driving. I've been trying to look for the thread regarding its fuel consumption. Kaso di ko makita. Is it also true na mas matipid sa gas yung new models? 10km/li, is it possible na maging same yung consumption ng car namin sa new models. What adjustment need to be done? Your response is highly appreciated! Thanks!