I know some people are using already compiled clients, so I'm writing this tutorial to help change the font since jm2.me showed everyone how to change the font using the source. Not all fonts are usable by doing this, so try at your own risk.
First thing is open the LUNAClient.exe with a hex editor. Search for 2002 and you should find something like the image 2002_EYA.png.
The first 2002_EYA is the internal font name (find this by opening the font file in windows) of the ttf file you want to use. The second 2002_EYA is the file name of the font your using. Replace the 2002_EYA in both to whatever font you want.
For example, mine looks like the tahoma.png after I have altered it.
The ttf isn't required by most computers to be in the /Data/Interface/Windows/ location, but I would recommend it so other users can use the font you have chosen.
If you need help, post here. If this helped you, then +rep please :).

