Adding a delete/empty to a shopping cart

Using the following code, how would I add a delete and empty cart array to the shopping basket...I tried to define the session which is in bold.
<?php
include ('connection.php');

session_start ();

// define session variable
$_SESSION['cart'];

//if product exists in command line, add it to cart
@$id = $_GET['prod_id'];



//checks if command line has product added
if($id){
//checks if cart is empty & creates it
if(!isset($_SESSION['cart'])){
$_SESSION['cart'] = array();
$_SESSION['items'] = 0;
$_SESSION['total_price'] = '0.00';
}

//cart array contains productid & quantity - add
if (isset($_SESSION['cart'] [$id] ))
$_SESSION['cart'] [$id]++;
else
$_SESSION['cart'] [$id] = 1;
}
//remove
if (isset($_SESSION['cart'] [$id] ))
$_SESSION['cart'] [$id]--;
else
$_SESSION['cart'] [$id] = 0;
}

//checks if command line has product updated
if(isset($_POST['update'])){
foreach ($_SESSION['cart'] as $id => $qty){
//value from text box name
if($_POST[$id]=='0')
unset($_SESSION['cart'] [$id]);
else
$_SESSION['cart'] [$id] = $_POST[$id];
}
}
?>

<?php
//displays products
if (isset($_SESSION['cart']) && is_array ($_SESSION['cart'])){
echo '<div id="product">';
echo '<h2>My Basket</h2>';
echo '<table width="500" border="0" cellpadding=0 cellspacing=5>';
echo '<form name="userForm" method="post" action="sbasket.php">';
echo '<tr><td width="200" scope="col" align="center"><h2>Product: '.$id['p_name'].' </h2></td>';
echo '<td width="150" align="right"><h2>Rental Wks: '.$id['qty'].' </h2></td>';
echo '<td width="150" align="right"><h2>Price/Wk: '.$id['price_wk'].'</h2></td></tr>';
$_SESSION['total_price'] = '0.00';
$_SESSION['items'] = 0;

//place lines of products in page
foreach ($_SESSION['cart'] as $id => $qty){
$query = 'select * from products where prod_id = '.$id.' ';
$result = mysql_query($query);
if (!$result){
mysql_close($conn);
return -2;
}
$catNo = mysql_num_rows($result);
if ($catNo == 0){
mysql_close($conn);
return 0;
}
$product = array();
$product = mysql_fetch_assoc($result);

$tprice = $qty*$product['price_wk'];

echo '<tr><td align = "left"><h2><span>';
echo $product['p_name'];
echo '</span></h2></td>';
echo '<td align = "right"><h2><span>';
//name of textbox=prodid and value=qty
echo '<input name="'.$id.'" type="text" size="3" maxlength="3" value="'.$qty.'">';
echo '</span></h2></td>';
echo '<td align = "right"><h2><span>&pound;';
echo $tprice;
echo '</span></h2></td></tr>';

$_SESSION['items'] += $qty;
$_SESSION['total_price'] += $tprice;
}

//starts the update qty proceedure
echo '<input type="hidden" name="update" value=true>';
echo '<tr bgcolor="#999999"><td align="center"><input type="submit" name="Submit" value="Update Shopping Basket"></td>
<td align = "right"><b>Number of Wks: '.$_SESSION['items'].'</b></td><td align="right"><b>Total Price: &pound;'.$_SESSION['total_price'].'</b></td></tr>';
echo '</form>';
echo '</table>';
echo '</div>';

}else{
//if no product in cart
echo '<div id="information">';
echo '<h3><span>No products in Shopping basket</span></h3>';
echo '<p class="p1"><span>Please login and add products to your shopping basket</span></p>';
echo '</div>';
}


//further options
echo '<div id="product">';
echo '<h3>Further options</h3>';
if(isset($_SESSION['loggedUser'])){
echo '<form name="furForm" method="post" action="finalizeorder.php"><input type="submit" name="Submit" value="Finalize Order"></form>';
}
else{
echo '<form name="furForm" method="post" action="register.php"><input type="submit" name="Submit" value="Please login to finalize your order"></form>';
}
echo '</div>';
?>