To change your font on your ENTIRE forum (with the exception of images that contain text)
add these
to your CSS

Code:

th
{
font-family: cursive;
}

*
{
   
font-size:12px; 
font-family: cursive;
}

TO get to your CSS style sheet goto:
acp> display>Colors (left side)> CSS (in the center)
and paste the above code there!
if you dont want it cursive you can use:
Arial,
Helvetica,
sans-serif
times,
Tahoma
Verdana
and many more just google CSS FONTS to see what you can use!