Hi,
1. To change the image of the Payment method, you can upload you picture in the folder "media\com_hikashop\images\payment" , then in the payment method configuration page, click on the edit icon for the "Images" option and select your picture.
2. You can edit the mail "order_creation_notification" and replace the line:
echo JText::_('ORDER_VALID_AFTER_PAYMENT');
By something like:
if($data->order_shipping_method == 'collectondelivery')
echo JText::_('ORDER_VALID_AFTER_PAYMENT');
else
echo JText::_('ORDER_VALID_AFTER_PAYMENT');
3. You can edit these views in HikaShop > Display > Views, the file "order / invoice". Then change the translations.
For the text size, you can change it in the Frontend CSS File in HikaShop > Configuration > Display.
4. There is maybe a JavaScript error due to another component or your template. Can you check if an error appear (you can press F12 when in your explorer) ?
Are you using IE 7 ?