I wouldn't sugget doing this unless you are extremely confident in your skills. I've been modding cars for quite some time and I can change out the motor or transmission if I cause any problems.
If you have the skill and resources. Then you would start by getting a tuning program such as SCT PRP, Sniper or Tweecer to learn the tuning ropes, then once you have a quality Wideband O2 sensor to monitor how lean you are, you start to tweek the AFR to run lean under a light throttle cruise.
The Zetec motor seems to respond well to running lean
