Redmine

I want to customize e-mail notification format.
So I modify C:\Bitnami\redmine-3.4.6-5\apps\redmine\htdocs\app\models\ mailer.rb and restart Bitnami Redmine Stack.
However, my update is not applied to e-mail notification.
How can I apply my mailer.rb modification to my redmine?

for example, I updated mailer.rb like this:
(from)
def test_email(user)
set_language_if_valid(user.language)
@url = url_for(:controller => 'welcome')
mail :to => user.mail,
:subject => 'Redmine test'
end

(to)
def test_email(user)
set_language_if_valid(user.language)
@url = url_for(:controller => 'welcome')
mail :to => user.mail,
:subject => 'mailer.rb update test'
end

Please help me!