Hi,
You'll have to edit the file show_products via the menu Display>Views
There, you can remove the line:
echo '<br/>'.JText::sprintf('PLUS_X_OF_VAT', $this->currencyHelper->format($product->order_product_tax, $this->order->order_currency_id));
And change the line:
<?php echo $this->currencyHelper->format($product->order_product_total_price, $this->order->order_currency_id);?>
to:
<?php echo $this->currencyHelper->format($product->order_product_price*$product->order_product_quantity, $this->order->order_currency_id);?>