If i change my air filter to a K&N filter, would i see and real changes in the cars performance, or is it not worth the changing.

Not worth

Any gains would be barely noticeable as you'll just get slightly quicker airflow. The main benefit would be not having to ever change the filter again for the life of the car but you will most likely need to clean it once or twice, and re-oil it. The guy I go to for service reckons just changing the regular filter every service would do just as good. Fit a good brand though, not made in china out of old tea bags type of thing.  Unless of course, you just fancy the K&N... I have one on a Yaris and its perfectly fine. Never bothered for the Fabia as I've never seen one at a good enough price so always replaced with Bosch or similar.