You will find that on your Account/E-Mail Preferences page (link to that is on your Start page). Scroll down to the "How My Daily Calorie Range is Determined" section and you can change your option there.
Hope this helps!
"I am only one, but I am one. I cannot do everything, but I can do something. And I will not let what I cannot do interfere with what I can do." Edward Everett Hale