Change required field text

At the top of the forms is the text “fields marked with a * are required”

I want to change this text but cannot seem to figure out how.

I found the line in includes>display>form>required-label.php
and changed the text there, but wordpress tells me this file is inactive, and when i saved the changes, the text on the form did not change (probably bc the file is inactive).

Where can i change this text so it will actually take effect?

http://wordpress.org/plugins/ninja-forms/