from what i know about ecu units and car electronics, you can't change the ecu for a "more powerful" one. in order to get more power out of your 1.4, you'll have to apply some other tuning methods to it. such as the oh-so-popular "chipping the inlet temperature sensor" technique, along with an induction kit, usually gives a fair bit of extra power. there's a haynes manual all about modifying a car, including tuning it, and there's bound to be other information hanging around the net, and surely some other people on this newsgroup know their power-tuning inside out too!
dan