How to delete tabs in V 1.8

Code:

var avacweb_chat_config = {
  version : '1-8',
  new_chat_title : 'AvacWeb Chatbox',
  auto_log_in : 'open',
  archives : 1,
  sound_file : 'http://www.freesfx.co.uk/rx2/mp3s/2/1305_1256857800.mp3',
  stylesheet : 'http://chat.avacweb.net/avacweb_chat.css',
  disable_timeout : 0,
  allow_private_messaging : 1,
  allow_user_resize : 1,
  commands : {},
  can_open_tabs : [1], //user ids of users who can open new tabs.
  tabs : {},
  allow_copyrights : 1, //please be kind and allow AWC to place small discreet copyrights and backlink on your forum.
  // DO NOT TOUCH ANYTHING BELOW
  message_hook:[],user_hook:[],events:{},add_event:function(t,f) {t=/^on/.test(t)?t:'on'+t;t in this.events?this.events[t].push(f):this.events[t]=[f]}};
document.write('<script type="text/javascript" src="http://chat.avacweb.net/v' + avacweb_chat_config.version + '.js" id="achat_script"></script>');

How can I set it up to delete some tabs.

the line
tabs : {},

means that there are no special tabs.. so what do you want to delete? o.O

Clear the chat using "/clear" or "/cls", then refresh, to clear chat-box added tabs. I recommend you stick to adding tabs using the config (tabs : {}) rather than doing them via the chat-box.

Yes, chatbox added tabs only exist while there are messages for that tab. Therefore if you clear the chatbox there will be no messages for that tab and therefore it will not exist.