Hi I found the solution. Go to your odoo installation path, find odoo/server/openerp/addons/website/static/src/js/website.editor.js

in website.editor.js  find the code below and replace the values of 5 as you wish

onBlock: function (panel, block) {

block.autoSize = true;

block.element.setHtml(openerp.qweb.render('website.editor.table.panel', {

rows: 5,

cols: 5,

}));