Add this to your additional.css
Code:
/*Start center avatar, username, title, rank in postbit legacy*/
.postbitlegacy .userinfo .username_container, .postbitlegacy .userinfo .rank, .postbitlegacy .userinfo .usertitle
{
text-align:center;
}
.postbitlegacy .userinfo .postuseravatar, .postbitlegacy .userinfo .postuseravatar img
{
float:none;
text-align:center;
}
.postbitlegacy .userinfo .usertitle
{
display: block;
float:none;
text-align:center;
clear: both;
}
/*End center avatar, username, title, rank in postbit legacy*/