How to change fuel air mixture?

[FacELesS.]

I have an 1.4i citi golf and noticed that my fuel air mixtures is too rich. How would one change the FAM? Do you have to send it in to a garage? If so, how much will something like that cost about?

 

[Highflyer_GP]

This usually occurs when people replace their standard air filters, you did that didn't you?

Anyway have your CO levels adjusted. Don't think that it costs too much to do.

 

[FacELesS.]

Everything looks like stock components, but I don't know the exact history since I bought it 2nd hand.