Where do I change that email
 
"Dear .., you were succesfully blablabla"
 
Jeez, why isn't everything at the right place!?

It is in the "right" place - its just you dont know where it is
 
Lets start from the beginning. What is it the customer/user has done or wants to do that means you have to send an email?
 
Someone might then be able to suggest how you can tailor the response.

If someone registers they gets that email. It contains their username and password..
 
And its not in the right place :P

So they are registering to become a site user and can have a choice of registering for different user types?
 
In "Site Users" there are "User Types" and in the "Profile Section" of each type theres a tab for "Registration Notify" which sends the user/pass email message.
 
Circuitous logic perhaps?