how change the message when complete account

-- url of the page with the problem -- : kosmima-gkiotli.gr
-- HikaShop version -- : 2.4.0
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.3.1
-- Browser(s) name and version -- : firefox 38.0.1

hi,
I would ask you how can I change the displying message which appear when the user completes their account. For example now is appears the follow:

Message
Your account has been created and an activation link has been sent to the e-mail address you entered. Note that you must activate the account by clicking on the activation link in the e-mail that you receive before you can login.

I would appear something like this:
Message
Your account has been created and an activation link has been sent to the e-mail address you entered. If it hasn't sent to the mail check your spam area or call as on phone. Note that you must activate the account by clicking on the activation link in the e-mail that you receive before you can login.

Thanks in advance

Thank you!!!