Q. How do I change the weighting of the Quarters and Final Exam?

A. In the Gradebook, click on details and scroll to the bottom of the page.
     The default for Q1, Q2, Q3 & Q4 is 2.25 and for the Final it is 1.0. 

If default were able to be define in Aspen, enter 4.5 for Q1 and Q2 and 1.0 for the final exam.
Aspen automatically takes the default setting for full year courses and applies it to semester courses. There's no way to create a default for semester courses alone.
 For a semester course, if you are providing a final Exam you need to change the weighting of the terms as seen below.

Weighted Avg Sem