Since your in Norway I assume your bike is fuel injected. Jetting is for carbureted bikes. You would need fuel mapping.
Jetting/mapping adjusts fuel for horsepower or gas economy, etc..
In a nutshell when changing an exhaust system or intake you are making the bike breath more therefore leaning out the air/fuel ratio. You change the jets on the carburetor or in your case change the fuel map to combat this.
Generally bikes come out of the factory lean for emissions purposes. That's why a person would jet/map a stock bike.