How to edit admin new account email

If a store is set so the admin gets an email upon registration of a new account, the admin gets an email like the following:

"A new customer has signed up:

Web Site: XXXX First Name: XXXX Last Name: XXXX Customer Group: XXXX
E-Mail: XXXX@XXXX.com
Telephone: XXXX


Address:


Tax ID:
Address 1: XXXX
Address 2:
Post Code: XXXX
City: XXXX
Country: XXXX
Region / State: XXXX"

I need to be able to edit this so that it is set out a bit differently, but I can't work out where the .tpl file is for this.
Can someone point me in the right direction???

Thanks!

sending mail is in model, \catalog\model\account\customer.php

Thanks Dian,

I've had a look at that and the accompanying language file and have successfully made SOME changes.
But I am struggling on one thing. Perhaps you can help?

I would like to add line breaks between the information shown below:
Web Site: XXXX First Name: XXXX Last Name: XXXX Customer Group: XXXX

so that it is displayed as shown below:
Web Site: XXXX
First Name: XXXX
Last Name: XXXX
Customer Group: XXXX

Do you have any idea how this can be achieved???

Thanks.