data folder of your mugen, select.def (or your motif folder if you use a custom motif).
open it via notepad, then tap F3 and search for these:
;Character select definition
then somewhere under these lines you will find:
p1.name.offset = 10,162 ;Position to put name
p1.name.font = X,4,1
p2.name.offset = 309,162
p2.name.font = X,1,-1
where X is a number. this number determines which font to use on select screen for names.
after figuring the number out, scroll the System.def file up to its very top and look at files:
spr = system.sff ;Filename of sprite data
snd = system.snd ;Filename of sound data
logo.storyboard = ;Logo storyboard definition (optional)
intro.storyboard = ;Intro storyboard definition (optional)
select = select.def ;Character and stage selection list
fight = fight.def ;Fight definition filename
font1 = f-4x6.def ;System fonts
font2 = f-6x9.def ;System fonts
font3 = jg.fnt
fontX = ...
where X is the same number you found out. it will direct you to a def or fnt file you need to edit in Font folder of your mugen. def type fonts change size easily, while fnt fonts can be edited via Font Factory