Change font type

Hi,

Can you advise how to change the type of the font? This is my blog eskaner.pl/blog.
I am getting in trouble every time I am using Polish fonts i.e. title of the post “Słowem wstępu”. You can see they are visibly different from the other letters. I was hoping I could change headers to Arial or Verdana that recognises Polish fonts but so far I failed miserably. Please advise.

Thanks,
Olka