the font is too small

Open style/<style name>.css

Locate: .pun {FONT-SIZE: 11px; LINE-HEIGHT: normal}

Change FONT-SIZE to whatever you want.

Also, have a look at these:

/* 2.3 Font size for headers */

.pun H2, .pun H4 {FONT-SIZE: 1em}
.pun H3 {FONT-SIZE: 1.1em}
#brdtitle H1 {FONT-SIZE: 1.4em}

/* 2.4 Larger text for particular items */

DIV.postmsg P {LINE-HEIGHT: 1.4}
DIV.postleft DT {FONT-SIZE: 1.1em}
.pun PRE {FONT-SIZE: 1.2em}