The easiest way would be to find a font you like (on DaFonts for example) and rename it "smog" after you've placed it in the right folder.
(PokeMMO/data/themes/simplesmog/res/fonts) - otherwise you'd have to do a search in all the (.xml) files (opened in a program like notepad++) and change each "smog" font to the name of the font you'd like, the first option definitely easier!
Hopefully that was an easy enough explanation, enjoy!
Edit: I should also note that if you're comfortable enough opening up the .xml files, doing a search of all within notepad++ (ctrl+f, search all open documents) for "smog" you'll be able to recolor the text (with html color codes) and realign or center certain texts if you'd like.