Changing the default text

Hi - would you please advise which php files I would need to edit to change the default text:

"If you have a coupon code, please enter it below"

and

"A coupon discount in the amount of $XXX will be applied to your order. (See "Order Summary" at bottom of page)"

Thanks.

for the first text:
www/administrator/components/com_virtuemart/languages/common/[english].php

for the secont text, I am not familiar with that text. Where do you see it?

second text is shown after submitting a valid coupon. I'm also using the one page checkout by polished geek.

Yes that text is within onepagecheckout module. In its root directory look in
coupon_ajax.php:
you should see