[Aken]

Assuming you're referring to the postbit_legacy styling, open the posbit_legacy template and find:

			<if condition="$show['avatar']">
				<div class="smallfont">
					&nbsp;<br /><a href="member.php?$session[sessionurl]u=$post[userid]"><img src="$post[avatarurl]" $post[avwidth] $post[avheight] alt="<phrase 1="$post[username]">$vbphrase[xs_avatar]</phrase>" border="0" /></a>
				</div>
			</if>

Replace with:

			<if condition="$show['avatar']">
				<div class="smallfont" style="text-align: center;">
					&nbsp;<br /><a href="member.php?$session[sessionurl]u=$post[userid]"><img src="$post[avatarurl]" $post[avwidth] $post[avheight] alt="<phrase 1="$post[username]">$vbphrase[xs_avatar]</phrase>" border="0" /></a>
				</div>
			</if>