Unable to locate area to change text

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.3
-- PHP version -- : 5.5
-- Browser(s) name and version -- : Mozilla Firefox 39.0

I am trying to change the wording Common Price next to the retail price field to usual retail price but I can't find where I go to do this I have managed to locate it in firebug and change it to how I want there. I have attached the as it is and how I want it screengrabs. Can you help me in finding the place to update this please? Many thanks for any help you can offer.

Thank you ... I much appreciate your help!