Change CSS tag by code

I have been given by a designer the HTML show below. This is a menu which will be used in throughout our website in a master page. My worry is how can I handle de the different class used depending when the page is selected or not. Below when on the page the id is "bot_seleccionado" and when a page is not selected it is bot1.
<table border="0" align="right" cellpadding="0" cellspacing="0"> <tr> <td><span id="bot_seleccionado" > Inicio</span></td> <td><span id="bot1"> <a href="Empresa.aspx">Empresa</a></span></td> <td><span id="bot1"> <a href="Servicios.aspx">Servicios</a></span></td> <td><span id="bot1"> <a href="Licitaciones.aspx">Licitaciones</a></span></td> <td><s ...