PHP Code:
#Counter 

   $result = @mysql_query("SELECT * FROM users WHERE username = '$_COOKIE[loggedin]'"); 

while ($usr = mysql_fetch_array($result)){ 

   $addtonumbers = $usr['numbers'] + 1; 

  @mysql_query("UPDATE users SET numbers = '$addtonumbers' WHERE username = '$_COOKIE[loggedin]'"); 
} 
that should work for you. If of coarse those are teh fields used