Q1: You can recreate the tables with the recreate-xlrstats.sql file.
This file is available in your b3/docs/ folder or on the
www.XLRstats.com website in the download section.
Or you could empty the tables with a mySQL tool or front-end like phpMyAdmin.
Q2: Have you checked out the statsconfig.php? Find:
// Number of players/maps/weapons in mainpage top lists
$toplist_max = 20;
$maplist_max = 25;
$weaplist_max = 10;
and change them to your liking.