in memberlist_resultsbit template find:
Code:
<img src="$avatarurl" border="0" $avwidth $avheight alt="<phrase 1="$userinfo[username]">$vbphrase[xs_avatar]</phrase>" hspace="4" vspace="4" />
Replace with:
Code:
<img src="$avatarurl" border="0" width="50" height="50" alt="<phrase 1="$userinfo[username]">$vbphrase[xs_avatar]</phrase>" hspace="4" vspace="4" />
change
50 to what fits your forum ^_^
Regards