You would modify the register_rules template. Look for this part:
HTML Code:
<div class="page" style="border:thin inset; padding:$stylevar[cellpadding]px;<if condition="!is_browser('konqueror')"> height:175px; overflow:auto</if>">
<if condition="$show['coppa']">
<!-- coppa regulations -->
<p><strong>$vbphrase[coppa_policy]</strong></p>
<phrase 1="$vboptions[bbtitle]" 2="$vboptions[forumhome].php$session[sessionurl_q]" 3="register.php?$session[sessionurl]do=coppaform" 4="$vboptions[webmasteremail]">$vbphrase[coppa_rules_description]</phrase>
<!-- / coppa regulations -->
</if>
<!-- regular forum rules -->
<phrase 1="$vboptions[forumhome].php$session[sessionurl_q]" 2="$vboptions[bbtitle]">$vbphrase[forum_rules_description]</phrase>
<!-- regular forum rules -->
</div>
And modify the first div statement. You may want to try removing it of removing the height/overflow part of the style. (If you remove the div tag altogether, don't forget to remove the ending div tag.)