Hi taha you can go to site using ftp and go to themes which ever one you are using then in base.css go to base elements you will see the font there all you do is change that to what ever you want but remember to use a decent editor like notepad++
save and your done

in fire fox and chrome its ok .. but in IE it doesnt show the tahoma ... :(

You can use this website to change the fonts of your website. It helped me a lot and I am sure that this fancy number font generator will also prove pretty helpful for you. 

TO change your simple text into cool and stylish font styles you must need to use font changer that will provide you quality options.

Regards: fbdownloader