Go into the Admin CP and to Styles & Templates and edit each of the parent styles for 'FORUMHOME'
search for
<if condition="$show['guest']">
<!-- guest welcome message -->
<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
<tr>
<td class="tcat"><phrase 1="$vboptions[bbtitle]">$vbphrase[welcome_to_the_x]</phrase></td>
</tr>
<tr>
<td class="alt1">
<phrase 1="faq.php$session[sessionurl_q]" 2="register.php$session[sessionurl_q]">$vbphrase[first_visit_message]</phrase>
</td>
</tr>
</table>
<!-- / guest welcome message -->
<br />
</if>
and either remove it or comment it out.