How do I change the wording of WordPress's default activation emails?

Hi,

I want to change the wording of the activation email sent out when you sign up for a store on my site. I want to change it from saying.

“To activate your blog” to “To open your store”.

I also want to pretty it up which I understand the HTML Email Templates plugin will do but will that allow me to change the content?

Regards,

Nat.