Snippet menu using jQuery and PHP
Reasons not to substitute Javascript for PHP

If you use Javascript (including jQuery), then your site won't work if Javascript is disabled.  

To use Javascript, you have to give unauthenticated users the same information as authenticated users and even admins.  Someone can save the HTML and edit it to show the full information.  This doesn't matter much with a menu, but with data...  

Formatting


&lt;?php
  session_start(); 
   if(isset($_SESSION['Usuario']) and $_SESSION['estado'] == 'Autenticado')                     { ?&gt;
    &lt;a href="Navegacion/Cuenta.php"&gt; &lt;?php echo $_SESSION['Usuario'];?&gt; &lt;/a&gt;
    &lt;a href="Navegacion/Carrito.php"&gt;&lt;img src="Images/Carrito.png" alt=""  width="20" height="20" &gt;&lt;/a&gt;
    &lt;a href="Navegacion/Php/Logout.php"&gt;Salir&lt;/a&gt;
 &lt;?php }    
    else {    ?&gt;
        &lt;a href="Navegacion/Entrar.php"&gt;Entrar&lt;/a&gt;
        &lt;a href="Navegacion/Registrarse.php"&gt;Registrarse&lt;/a&gt;
&lt;?php   }    ?&gt;



I find your use of beginning and ending tags confusing.  Consider 

&lt;?php
  session_start(); 
  if (isset($_SESSION['Usuario']) &amp;&amp; $_SESSION['estado'] == 'Autenticado') {
?&gt;
    &lt;a href="Navegacion/Cuenta.php"&gt; &lt;?php echo $_SESSION['Usuario']; ?&gt; &lt;/a&gt;
    &lt;a href="Navegacion/Carrito.php"&gt;&lt;img src="Images/Carrito.png" alt=""  width="20" height="20" &gt;&lt;/a&gt;
    &lt;a href="Navegacion/Php/Logout.php"&gt;Salir&lt;/a&gt;
&lt;?php
  }    
  else {
?&gt;
        &lt;a href="Navegacion/Entrar.php"&gt;Entrar&lt;/a&gt;
        &lt;a href="Navegacion/Registrarse.php"&gt;Registrarse&lt;/a&gt;
&lt;?php
  }
?&gt;


By always putting tags at the left margin, it is easier to see where code blocks begin and end.  Only the embedded output has the tags inline as well.  This will look more familiar to most people who might edit your code later.