you can find the file in /components/com_invoices/views/invoices/tmpl/default.php . if you're familiar with HTML (and maybe a little PHP..) it will be very easy for you to remove what you don't need. just.. be careful to not mess things up! I recommend to make a backup copy of that file first.

Thx so much. I will give a try.

Seems I can't do it after I commented out those lines. I want to take out payment date time. Can u let me know which lines I should comment out? Thx.

I have taken out the following lines from the php:

payment->payment_datetime == "0000-00-00 00:00:00") echo JText::_('NOT_SETTED'); else echo JHTML::_('date', $this->payment->payment_datetime, JText::_('DATE_FORMAT_LC3')); ?>

I have tried taking out these lines from the default.php under invoices folder and payment folders but still does not work. It still shows on the front-end at the My Payment Section with the payment_datetime.

can u advise what i have done wrong?

you're in the wrong file...

this code you post is from the payment/tmpl/default.php file, which is NOT the one you have to modify.
the only file you need to modify is invoices/tmpl/default.php, it's around line 181...

THanks so much. I figured out now, and it worked now.