If you mean this forum, increase zoom level in your browser to 110% or 120%
If you mean your own forum, edit the index.css file for default theme...
Find:
body
{
background: #E9EEF2 url(../images/theme/backdrop.png) repeat-x;
font: 78%/130% "Verdana", "Arial", "Helvetica", sans-serif;
margin: 0 auto;
padding: 15px 0;
}
Replace with:
body
{
background: #E9EEF2 url(../images/theme/backdrop.png) repeat-x;
font: 88%/130% "Verdana", "Arial", "Helvetica", sans-serif;
margin: 0 auto;
padding: 15px 0;
}